When I am the one with problems

Hi, this is more of a rant rather than specific question, but I would appreciate some advice. Since a few years ago when I came out, after I dealt with my own problems like coming out to my parents, being open in HS, being single and not having the same experiences as my straight friends, I became a really positive person, I tried to see the positive side in things, help my friends when they had problems, give some advice here on this subreddit, mostly because after a few years of problems I came to the realization that it’s stupid to live all your life being a negative person, you obviously have bad days and problems, but it’s always better to tried to deal with them and be more positive about the future. However, since I started university, all of that started to “shake”, even though I became a more social person, more open to meet new people (I made friends in a few days, something that in other times took me weeks) but something totally different happened this time. I met another gay guy (I wrote another post a few days ago about that), and that changed everything. I’m trying to be friends with him because he has a boyfriend and I don’t want to mess up with that, but all those bad feelings of being alone came again, and now worse, since I met someone who has what I’ve been wanting for years, I’m not angry at him or something like that, I’m just sad because I’m alone. I know I’m probably overreacting, I’m really young, just started university and all of that, I’m living in a supportive place where finding other gays is easy, etc, I know those things, I said those things to others, but now it happened to me. So if somebody reads this, I would appreciate your advice on being single for a long time and feeling lonely. Thanks