My [26/m] bf [23/m] wants an open relationship. He says he doesn't want it if I don't like it? I don't like it and I don't know what to do now?

I'm a gay guy in a closed relationship and recently my boyfriend (23m) told me (26m) that he wants to try open relationship. When I asked him the reason, he said, he doesn't know and just wants to try. This is my first relationship and we've been on for slightly over 2 years. He had been in relationships and on sex dates before our relationship.I figured that something has been troubling him (he got lost often, he got mood swings) since the last 8 months and I've even asked him, if he feels like seeing other people? He said no and denied it back then but now he says he wants to open up. I told him that, I don't like the idea of open relationship, but if he wants it I don't want to stop it either.Also I went into depression a few months ago when I found that he had an account on a dating and hookup site. I was prescribed xanax for a while. I didn't tell him about my depression but when he found out, he said that he was just making friends there and quit his account and told me he's not going back. But when we had this talk a few weeks back, he told he's back on that site making friends. So, I said we can have a platonic relationship without having any sex or kiss and that we'll be there for each other with other forms of intimacy intact. I also said, I want him to do the things he wants to do without feeling bad and that I'll help him in it if he wants to. He laughed when I told him, I can help him see other people. I can't imagine a life without him and he told me the same. He said he want us to get married and have kids and told me that this open-relationship is just a phase and will become closed after a while. I told him, I can't open up the relationship and close it again because, if opened, I won't be able to look at him the same way I used to and so we'll proceed with a platonic relationship. Then he told me that, loosing the romantic intimacy with me for the open relationship is not worth it and said that he can't live without kissing me or holding me tight. I love him a lot but I feel like I'm a selfish blackmailer. I want him to be happy no matter what, be it with me or without me but I just don't like the idea of opening up the relationship. What should I do? I feel like he wants to see other people, but is not doing it for the sake of me. He told me now that he knows how to overcome it?! He is fighting against his own desires, wants and the love for me. What should we do? What should I do? I've never expected or demanded anything but I feel like he's trapped by my love and is not really free. I feel lost and I'm getting mood swings often now. I don't want to go into depression again. I love him a lot, and I'm ready to let him go, if he'll truly be happy. Advise me.I've conscised the above paragraphs here. We've been in a closed committed relationship for 2 years. We stay at two different places and hence used to meet every weekend or once in two weeks. I noticed something was wrong (he was getting mood swings) about a year ago. I kept asking him the reason and one day he mentions to me he's on a dating site making friends. I was ok with it initially but my insecurities began to grow and I went into depression. He found out about my depression 8 months ago and told me that it was just his way of letting out as he himself was having mood swings then (partially due to career, soul searching etc) and further said he wont go back to the site again. Our relationship was slowly getting back on track but then i noticed he was getting mood swings again often. Many times I asked if he wants to see other people, for which he said no (but I knew, he only said no so as to not disappoint me). Meanwhile his career took him far away and so we've been meeting once a month since July this year. I couldn't see him suffer (he was so lost during our phone conversations) and so to end his mood swings, two weeks ago, I went to his city, stayed with him over the weekend and asked him to tell me everything he hasn't told me yet because that is the only way his mood swings will reduce. Then he told me he wants to try open relationship. I know it already but I waited for him to tell it because I wanted him to tell it without feeling bad for me and finally he said it (still feeling bad). He also told me he is back on that dating site making friends. So I told him not to wait for/ask my permission to do what he wants. I further said that I can't be having a romantic relationship with him once I open up the relationship, because I'd never be able to see him the same way again. I love him a lot and he loves me the same way and we both know that we should spend our future (get married and have kids) together. Hence I suggested that we remain in a platonic relationship forever (even if we close the relationship again after sometime as he wanted) after opening up. For which he told me that losing intimacy with me is not worth opening the relationship and that he'll figure out a way to control his urges. But I feel like, I'm controlling/trapping/blackmailing him with my love by not letting him do what he wants. I don't want to lose him and he doesn't want to lose me. What should we do??!TL;DR; : Boyfriend of two years wants my permission for an open relationship. I don't like it and don't know what to do?!