Sometimes female friends will string a guy along as a distant option or just for the attention and validation, and even get jealous when they give or receive attention to and from other girls. They do this despite having no romantic or sexual interest. They might message him then ignore him when he responds, or take a while to respond with something, or ignore/snub him when she's with her "cool friends." These are also friends guys shouldn't be interested in romantically, or even as anything more than a casual acquaintance vs a true friend.

I'm not saying this is the case for your situation. It seems more like he's doing it for his own mental well being. Maybe(or maybe not) he can get over his feelings and be able to see you with other guys and talk about them without getting hurt or jealous. I would think the ideal thing to do would be to tell you the previous sentence, but that's easier said than done. I guess you could just pull him aside and tell him that you miss him as a friend, but that you'll give him space if he needs it. Then see in the future if you can both continue being friends, not just with your romantic disinterest, but his handling of the situation. But both of your feelings are valid, even if conflicting.