How to be happy with myself

Hello. Quick introduction:
I am 17 years old and workout 5-6 days a week. I study every day 1h(30min french and 30min math). I am my second year of high school and am just confused.

I used to date this girl who I really liked and who liked me back a lot. What we had lasted roughly 1 month. We broke up a year ago but we had a date yesterday and it went allright. After we ate she said she had to go home, my guees is because her best friend was feeling bad so she wanted to be with her. But I cant read minds can I?

Well, I am going throw some shit right now. Moodswings, low key depression and anxiety and just a lack of meaning? I dont know, something is missing in me and I feel bad.

Why did I mention my ex? Well, because she is the only girl I feel attracted to but at the same time shit just dont work. After being single for a year( that was my first gf) I feelt a desire for a relationship and I didint get it nowhere. I just cant seem to find a girl that likes me back or that I actually like. My high school is full of fucking dudes and I dont want to change my sexuality just to get a new relationship.

So, I only feel attracted to my ex who I see every day and who I feel I dont match with. I want but at the same time I dont feel ready for a relationship so I ask this.

How do you guys fill the hole? How do you guys deal with being single? I am problaby just having a bad week and my brain is mistlikely healing from all the PMO so therefore I feel like shit but I would like to hear your opinion.

Thanks!