[20/f] FWB with my ex (22/m)?

Hey hey, so my boyfriend of four years broke up with me just under a month ago. He was emotionally closed off (he stopped saying I love you, wouldn't tell me what was going on with him so when he said he was going through depression toward the end of our relationship it blindsided me completely), and needed to figure things out in his life. It left me really shocked and pretty heartbroken.

We've been trying to normalize a friendship, but less than a week ago he told me that he'd made a huge mistake, that he pushed away the best thing in his life, and he wants to be with me, but he understood if I couldn't commit again. For me, I can't. I feel that there are some things in his life that he needs to work out before I feel like I can go back; if I went back now, I feel like the same thing would happen. He knows that and understands that.

Last night we had dinner at a cafe we go to together regularly, and we ended up hooking up. I wanted to, he wanted to, no pressure, no coercion. Afterward he reiterated he wanted to be with me, but understood if I still felt I couldn't come back. I told him that I couldn't, but that I wasn't opposed to hooking up again. I told him I don't want him to feel like I'm using him (because I'm not. I still legitimately enjoy being around him, having him in my life, etc. It's not all for sex), I didn't want to him to feel pressured to do anything, I wanted everything to feel comfortable. He said he knew I wasn't using him or pressuring him, he wanted to be FWB as well. He understood I can't feel comfortable committing again. We also established that we'd be open about who we are seeing; I told him I'd been talking to a guy that I ended up cutting off, he admitted he's been on a date. So it seems like a pretty solid agreement overall to me.

But something still doesn't feel right about it. Before he left, he told me he hoped this was a way for me to ease him back into my life as a partner again. For him, I feel like the FWB end goal is to be together again. For me it's not quite that way. I still have feelings, in a perfect world I wish we could work out right now. But there are simply things that need to be fixed before I could feel comfortable going back and committing. I am, however, not going to wait around for him to fix those things. I am going to move on if it feels right.

Is this ethical? Does this sound like it'll blow up in my face? I still care about him tremendously, am I just going to hurt him the more we do this and not get back together? There's a part of me that feels rotten over doing this, but he wants it, it's consensual. Any advice and similar stories would be appreciated.