I haven't really had to face this too much. Most of the time A and I have either been in triads, one long term. and even then it was me and the other or all of us together when it came to sex. (they did spend a lot of time together out of bed, and I am sure there was some physical affection, or at least I hope there was. I will have to ask A.) Or Vish relationships with me as the hinge.
Only once has A been the hinge in a V and it was extremely short lived. We had led up to it for months online. When they finally managed to get together rl it happened to line up with my semi-annual trek 3000 miles with kids to see my parents. I was so busy I didn't have time to do much more than call him twice a day to check in. Never even thought about worrying about it. Very shortly after that she (lady A was with) had a very serious health crisis. It stopped everything but friendship and love (no sex of any kind cold) we stayed in touch until she passed away. Hard emotionally but not in the same way.
But I have never had to face me sitting at home, alone, wondering about it. I will have to think about that. I want to think I would be fine. Hmm
Jealousy, that dragon which slays love under the pretence of keeping it alive. -Havelock Ellis