I think he was quite clear in his intentions. Yes, not completely clear. But clear enough. If he says 'I don't see anything happening romantically, but never say never.' and then in the months following you still stay good friends but nothing romantically happens, then that is your answer. He wants to be friends but nothing more.

Now I see someone reply that he wants you to stay single and that he is manipulating you. I don't know why this interpretation is so. But of course you also suggest he may be playing games. The only thing he can be blamed for is to not tell you 'Look, we are friends, but we won't be partners. Go out and find your romance.' But does he really need to say that to be a good friend? Perfect friend, maybe.

As for him stringing you along. I don't think it is clear that he kept suggesting that something romantic may happen somewhere down the line. It seems that only when you pressed him on it, he said something about it.

Him not being in love because he is in love with someone else? Him not being in love with you because he is depressed? Not a complete impossibility. But do you really want to keep waiting for him? His brain chemistry didn't trigger. There is no reason to assume that something is going to change that is going to trigger it.

As for being friends with someone you are deeply in love with, I am supposed to be able to say something wise here, because of experience. But no. After all these years, I am still clueless about what it means to me. Let alone to you.