I think if they’re dating someone else it is just part of the journey you have to walk right now. I don’t think you have to be cellibate or stay single yourself in fact it’s probably better that you don’t just wallow and focus on them. It isn’t the end of your story, but don’t just sit waiting for them to break up.
If you do that, they’ll immediately end up with someone else because you’re still not ready.
Karmic relationships are preparation. I spent 10 years with someone else after my twin, and I both ran, and honestly, those years did more work on me than I understood at the time.
We get what we need, not what we want, until we’re actually ready for both. Your heart has to be prepared to hold that kind of energy. The karmics, the soulmates in between… they’re doing work on us whether we realize it or not (and usually we don’t, not until way later).
The longing just stays. Try to shift your focus, but your twin never really leaves your heart. You just learn to carry it differently.
You can distract yourself but (like others have said) the loop of separation just keeps going until you actually do the work.
The connection doesn’t disappear. Even when you’ve logically moved forward and found peace with where everything landed, they’re just… there. In your heart still. The readiness timeline depends so much on your twin’s sign. Mine’s a Scorpio, and that intensity means nothing moves fast when they’re not ready (like, nothing).
It hurts to think of them with someone else but I know that this is part of our planned blueprint and we both agreed to it. This is so they can learn from them and I have the space to do what I need to do. It will be worth it.
Your ascension doesn’t depend on where they sleep at night. Loving without conditions means releasing attachment to outcomes, even when those outcomes feel like they should be yours. Nobody wants to accept that.
The energy is real. I’m not dismissing that. But their path toward growth might require exactly this experience right now. It’s not yours to redirect.
That whole ‘if you love something let it go’ thing is actually kind of real. I was a complete mess for days when I found out about his relationship, like I couldn’t function.
But keeping my distance ended up triggering something in him. He basically woke up to our connection and has been pursuing me ever since (even while still with her). His girlfriend is probably his karmic tbh.
Sometimes the soul contract includes a third-party chapter. Certain lessons just land differently without the intensity of union. Ask yourself what agreement you made to learn boundaries and self-worth here, and what agreement they made around integrity and choice. Two separate contracts, really.
For me it helps to focus less on the timeline (which will drive you crazy) and more on fulfilling my side of things cleanly.
Working directly with the nervous system is what helped me. I did EMDR for attachment wounds and EFT tapping when I would spiral about them being intimate with someone else. I also did cord-cutting meditations weekly, not to sever the TF bond but to clear the obsession and fear that were eating me alive.
I started inner child journaling too. Prompts like ‘What am I afraid it means about me?’ That one especially exposed the real trigger underneath the jealousy.
I had the agony of watching him with others, but knew deep down that it was temporary, low vibrational, and for his growth, not his long-term dream partner.
If it bothers you, those are traumas you need to heal. Understand that you are with me just finishing out lessons and soul contracts and those blocks will move when we do the work
I get you on the energy feeling mutual, but the external reality not matching that. That has confused me to NO end.
And the mixed signals. And not understanding how they can just turn away from that love and give all their energy, time and love to someone else while I’m just… sitting here trying to love him. And I have the extra layer of shared intimate space, energetically, so I can feel what they do as well 
And I cannot turn it off, neither can I turn off the love. So its a horrible place to be.
I’m at the point where… if we’re supposed to mirror the matrix twin’s action in “real life”, if he’s truly still dating, being romantic with another, maybe I should go out and do the same. I had no interest in another, or in dating itself right now as I’m in the middle of the divorce filing process, but its been YEARS since I’ve been with someone romantically. And 3 years since I told him I loved him. I’m lonely, and tired of sitting here restricted and ignored while he hangs out with other chicks and I can feel it, like its no big deal what that does to my heart.
Maybe experiencing someone who WANTS to be with me, likes who I am, CARES if I feel safe and happy, or if their actions hurt me, even just to have fun short term, would be a beneficial experience for me and lessen the focus on their activities.
But I think its harder for us spiritual twins, because we want to honor the purity of the energy we live in all the time. That love isnt something I’d easily act against, even though it seems easy for him. And I’d hate to hurt him if I was intimate with someone else and he felt it.
I agree with Megan4, that Karmic partners dont push growth, they simply accept them where they ARE without having to do the work. This means they feel more comfortable, as they are not forced to look at themselves, or heal, when with this other person. They accept the toxic parts of them, and their heart is in less danger if this person leaves too. However, this also means they are destined to repeat the same old hurtful patterns in their life. So its only a matter of time.
Anyway, hope by now your situation is in a happier place with your twin 
All we can do is love them, no matter what, focus on ourselves, and see where the journey takes us
This is exactly where I am right now. As I mentioned in my recent thread on energetic boundaries, I started dating someone recently who I really like and who likes me, and most importantly, is choosing me back. He does want to spend time with me; he isn’t running/avoiding/denying; he wants to share mutual romantic and sexual energy with me; he welcomes long hikes together and long conversations and just having fun in my company, as I’m having fun in his. And I know it’s not long term (or at least not forever); and I know this connection, however much I’m enjoying it right now, pales in comparison to my connection to my twin, on just about every level. I have been trying to honour the purity of my TF energy for a long time, and meanwhile he isn’t even recognising the power of that energy. He’s been dating various people over the past couple of years… he’s with someone at the moment (which is still causing me pain even as I know he’s choosing something safe and non-challenging while he heals). And my exploring this isn’t some kind of tit-for-tat - it’s just my recognition that I get to fully live my life too while he continues his growth and healing. And it definitely helps soften the edges of our current separation.
I don’t think this in any way interferes with the purity of our TF energy, because that is so far above any energy I could have with someone else that it’s basically in an entirely different category. And I realised last week that I have very much been waiting for him to show up and meet these needs for me… and that’s just not healthy energy to have around our connection. I don’t want any energy of need or lack between us when we finally unite. I want our union to come from a place of balance and from mutual desire for each other and our shared energy, not just desire for something that’s lacking in either of our lives.
So I’m finding a way to have those needs met for myself, and I’m reminding myself that there are people out there who want to be with me and who aren’t afraid to express that and to demonstrate their attraction, and that I don’t have to live like a goddamned nun until my TF is finally ready for this. That is deeply healing for me, on many levels.
And there’s also a part of me that is currently welcoming the prospect of a nice, safe, ordinary relationship that isn’t here to turn my entire world upside down. I know that won’t be enough for me in the longrun - I want the relationship that reaches into my core, fires me up from the inside, knows me in ways no one else possibly can, and demands that I am the highest version of myself in order to meet it - but right now nice, safe, and ordinary, (and not demanding growth at every turn) feels like a welcome respite from the intensity.