What is wrong with me

Help!!! So the beginning of my junior year I met a boy who was quite a bit older than me he was 19 and I was 16. When we started talking I never thought anything would come of it because he was my cousins bestfriends and he lived so far away, but as time went by I stayed catching feeling for him and I started driving to go see him and he drove down to see me. For the course of 5 months we were messing around together and I never new what we were. He would just call me his girl never girlfriend. So one day while I'm at school I look at his Snapchat story and it shows that he's with a girl and I think oh it's whatever he had friend who are girls I have friends who are guys but as I'm watching it they start kissing and making out and now I'm like wtf like I thought we were a thing. So I text him and he never responds he ghost me for 4 months before he apologizes and hasn't talked to me since. Ever since I found out about the other girl I haven't stopped thinking about him I always think about what if we were still together? Was it my fault that he thought that he needed another girl? Now keep in mind I was a junior at the time and now I'm a senior about to graduate and there has been other guys since him. Why do I keep thinking about this dude?? I'm I in love with him? Please help me to I can get over this guy and finally think about someone else.