I miss my friend

Okay so I had this friend who I had been in love with for years. He always rejected me and in the past I have confessed to him one time.
The big problem is that I always felt a deep connection between me and this guy. The second problem is that he preferes girls who are a bit underaged than him and I can’t understand this.
For 2 years he treated me like a piece of shit then for one year when I had drugs he sticked with me for a period of time, then he went to university.
Now he has a girlfriend who is smaller at age than him and I don’t understand why he chose her instead of me.
I still think about him and a few minutes ago I saw some pictures with him and her, theg went to visit his mom and the fact that I saw how happy they are made me feel like shit and I started crying because I know he will never like me and I will never find someone like him and nobody will ever like me.
I really miss him and the way we used to be when we used to hang out.
What can I do?