Help with moving on

Hey girls, I need some advice, I’ve liked this guy since i was 15 (I’m turning 18 in 2 weeks) we went to the same school and I even told him that I had feelings for him, I was told by people that he also had feelings for me but he’s just really shy to tell me, I waited for him to tell me but it never came so I decided that after high school I’ll move on because it wasn’t worth holding on to someone who wouldn’t like me back let alone notice me. Today he posted a picture of who I’m guessing is his girlfriend and him together. They look so happy together, and even though I told myself and my friends that I’m over him, it still hurt to see the picture and now I’m here crying about it, it hurts and I don’t know why, what should I do ?