Advice?

So I'm a high schooler in senior year right now (in the middle of senior year). I had a friend last year that has graduated and gone to university. I think she was more than just a friend to me but I didn't want to tell her because I thought it would ruin our friendship and because I'm pretty sure she's aromantic or asexual and that she didn't feel the same way towards me. Well, she's been gone for a bit more than half a year and I've been fine this whole time. Except this weekend, I talked to another friend and finally confessed to myself that I had liked her (the first one). Now I'm completely wrecked and I have no idea why. I haven't missed her like this until now. Can somebody help me and tell me why I'm feeling this all of a sudden?