Okay this might ruffle some feathers. When both twins are married, the universe is being pretty loud and clear. The union this lifetime is energetic. Mission-based.
That doesn’t mean it’s going to play out like a Hollywood movie, but I agree with the above. If you’re not happy in a marriage and looking at anyone else (your twin or otherwise) then get out of the marriage and give your spouse the freedom. Otherwise you’re just layering negative karma on yourself that you’ll never get away from in this lifetime.