I'm married and my best friend is in love with me. What am I supposed to do?

I was recently at a tail party with one of my closest friends I’ve known for a longtime, at least sixteen years. We were having a conversation about how he had split with his girlfriend and I commented on how he has had trouble getting into a long-term relationship since his wife died about seven years ago (his recent one has been his longest lasting a little less that two years and before that he seemed to be on a series of first dates with no second). I asked him if he still wasn’t over his wife’s death yet and he said that that wasn’t the case. He said that he just couldn’t give his heart to anyone else because he was in love with me. I was shocked. I’m married and we’ve never been romantically involved and I’ve never flirted with him or done anything intentionally to lead him on. He said, “I know you’re good girl and I know you love someone else and I don’t expect anything to happen between us. I want you to be happy and I know he’s given you everything you’ve wanted. I just can’t pretend that you mean less to me than you do”-something to that extent, I’m paraphrasing. The next day he called me and apologized for saying that claiming he had been tipsy and that he never should have said that and he hoped we could still be "just friends." I was semi-fine with it. It was kinda flattering and I figured I couldn’t tell him how to feel and he understood that I wasn’t going to start sleeping with him or anything. I wasn’t (and I’m still not) sure how we could go back to how things were before. I don’t want to emotionally disconnect, we’re still friends but I can’t escape the fact that he feels lovesick for me whenever we are together and I feel like I’m always watching myself wondering if I act too affectionate sometimes or questioning if I dress too y or flirt accidentally. And I'm starting to question if I have feelings for him. I don't know if it's in my mind or not. It’s driving me mad.