I have a very close male friend. In the past things were a bit odd - there was a time when things were very intense and borderline co-dependent, and during that time I had feelings that he knew about, but explicitly said he wasn't interested when I raised it one day. After that we didn't see each other for some time, during which time I met and started a relationship with DP. Friend has remained single apart from some short-term things that haven't gone anywhere.
We're friends again now which I really like as we get on well, but over the last little while the friendship has become quite intense again - near daily contact (largely driven by him), and seeing a bit of each other too, both in groups and one on one. I have been happy with this as value our friendship, am happy with it being just that, and feel that given what happened last time I am on safe ground to assume it's platonic on both sides. Yet as the intensity picks back up I'm finding myself feeling a little more nervous about it and worried things will get weird, especially as he made a comment last time I saw him about how taken by surprise he was that I moved on with DP so quickly. It's proving hard to pull back as he's in contact a lot, and I do get a lot from the friendship so don't want to withdraw for no reason. I'm also worried about him. He's much more unhappy than when we were friends previously, lonely and (I suspect) depressed. He's recently talked a lot about how his life hasn't panned out as he thought it would, and expected to be in a relationship by now.
For context too he doesn't have many other close friends, whereas I have many. DP knows the history and doesn't mind.
WWYD?