How to stop being depressed?

[Fort Lauderdale guy]

I am 18 and love my life and have great friends and stuff but I feel so depressed lately. I am stuck in this crappy job til May (quit in May) and will graduate high school then but i feel so down about girls. I keep making my decisions pretending I am going to be able to be to be with this girl who will be going to the college I work at. I don't know her but see her all over social media and went to school with her sister and know I need to move on. I won't be going to this college but will be in the same town. I know I will be happier if I focus on myself but it's just hard. Like I know I need to stop thinking about her and focus on myself and stop letting this stress me out so much.