Feeling Guilty Exploring Non-Monogamy, Advice?

I live with my bf of a year and a half, we are in our mid/latish twenties and we are wildly in love.

I'm not monogamous. I didn't know that about myself before I started dating him, and discovering it in the beginning tore us apart, because I lied to him and 'cheated' in that I broke the rules, though I didn't sleep with anyone without permission. I know this was wrong, I know I hurt him then, and I did and still do feel very, very bad for putting him through that unnecessarily.

It has been quite a while since then, and in the intervening time we were monogamous for quite a while, and I promised him that I could be happy that way. This was not true either, though I didn't know that until after. This was not an intentional lie, but I feel just as bad.

He did not leave me this time, and we are instead exploring non-monogamy in the form of threesomes and foursomes based around friendships. I am having so much fun. And he is being so generous in helping me to actualize my exploration.

But. I feel guilty constantly. I check in with him multiple times a day to make sure that his emotional well being is being monitored and not ignored out of hand, I check in during our sexual encounters and he knows that if he feels over whelmed I am happy to stop, reconnect with him, and do whatever he needs to feel secure with me. He is scared of giving me any kind of positive feedback, beyond admitting that he had fun, or enjoys the people we've met as friends, or thinks that a situation is hot, other wise, he won't tell me if he is happy with me or the larger situation, just that he would rather not be non monogamous and that being with me means he must be. He also says that he doesn't believe in monogamy at large- that there is no one else in the world who truly wants monogamy because he's never found it in another woman. I don't want to lose him, but I have said that if he would ultimately be happier, that he should look for a woman who wants monogamy-- which is when he protests that no such person exists. He also admits that maybe things can change and turn around, and he will become happy to engage in these activities with me, he just wants to make sure that I know that it's not what he wants right now and that right now he's not generally very happy about it. I feel like I do everything that I can to support him, I listen to him, I reaffirm my commitment and love for him, I remind him that I do not want any other partners but him, just the freedom to be sexually non-monogamous-- but this isn't enough. And when I try to suggest that he and I aren't a good fit, he just reminds me that everyone else in the world is non monogamous at heart and if he has to deal with it, he'd rather deal with it with me.

I don't know what to do. I do NOT want to lose him, but I can't stand to see him unhappy. I feel guilty constantly, because he says all these things but doesn't make an active effort to enjoy himself or think positively about the situation. It's killing me.

If anyone has any advice, I would really love to read some. Thank you to anyone who read all of this, and I hope that you all have a wonderful weekend.