I guess I should be more specific here...
He is supportive of my quad, meaning he is friends with all of us, but is friends with me the most. We have been friends for 4 years. My quad is unbelievably supportive of this relationship taking place. They know how much we connect, they all know I have a stronger connection with him emotionally than I have with the 3 of them, and all 3 of them are okay with this. Of course, small jealousies do occur, but we talk A LOT, all the time, about feelings. My friend and I have also talked A LOT about things, which is why he is taking some time to work on his own issues. I have flat out told him I can never be the center of his world as I am the center of no one's world. He understands this, and at least for now he is fine with it because he has other things to take care of, he has kids and a job that takes a lot of his time. My friend and I have talked many times about the quad and what it would mean for him and how he would feel. He never minds hearing about what is going on between us and has actually been helping me with connection issues I had been having between myself and my "boyfriend" of the quad.
The heartbreak factor, I meant MY heartbreak, not his, although I know both can happen. We have talked a lot about transitioning if the time came to go from being lovers back to friends again. It would be a huge lesson in compersion, but he is my friend, I would be happy for him to find happiness. I do not see our relationship ending by my hand, it would likely be because he found someone else.
We have already gotten very close emotionally which has led to some physicality, although not intercourse, thankfully. He has been the instigator in the situation and I have stopped things from going too far both times. Both times he has had second thoughts afterwards because he had thought he was ready and hadn't been. I have told him I wanted to go slowly and just strengthen our friendship, but it has been so hard because we literally have this magnetic pull to each other. It is something I have only experienced once before in my life. Because he doesn't want either of us to get hurt, he made the decision to take some time away from me. While it's difficult, I am in complete support of it because he is my friend and I want to see him be strong. He was in a very long term marriage with kids and hasn't really known any other relationship outside of his ex wife. His ex wife is an acquaintance of mine and I have to see her occasionally because of our kids.
Just for reference purposes, my husband and I have been married for 17 years and we have been in a quad for over 2 years. We have 3 kids between our quad.