TL;DR My ex boyfriend who broke up with me as he was against open relationships is now cool with it and wants to get back.

I dated J for 7 months and we both got on-board for an open relationship after 5 months of being exclusive. In the following week, I hooked up with a couple of guys (well within the rules that we framed) and it made him really uncomfortable. I get that it's harder for guys to hook up, but if he's not comfortable he must've been upfront. Things broke down and we had to break up.

Now, after about 3 months, he wants to get back together and promises that he's completely cool with an open relationship this time. He says "it just feels right and he has no answer to my "why suddenly". Ideally this seems okay, but the last month of our relationship was a tragedy, it was fights day in day out about the concept of open relationships and he ended it saying he was completely against it. I wonder what changed things now - what do you guys think I should go? Give it a go? I am tempted as he's a nice guy and very attractive. At the same time, don't want to go through the whole circle again as deep down i think he's not completely on-board and never will be.