Growing up and feeling stuck in myself

I just finished high school. I am scared of growing up, I am scared of the fact that even though I am 18 I still have the same issues of when I was 13, I am scared because I think I don't actually have any kind of eating disorder but I am just fucked up and it is my personality, so it will never get better. I don't have any kind of diagnosis and nobody knows; sometimes I just feel the need to get out of myself and lose control and I binge and I purge and sometimes I don't eat. It's not even frequent. But sometimes, everything just feels too much.

There is this guy I think I like, and sometimes I think we could be something, because I know he is kinda attracted to me, but he obviously likes my best friend more. The thing is, she is overweight. I rationally know it doesn't work like this, but I keep thinking that if he likes her and is somehow attracted to me as well, I must be overweight too. (I know I am not, and I am in an healthy weight, but I just can't stand watching myself in the mirror sometimes, and I know there are many fat people that are beautiful, but I am just fucked up like this). Also, this is horrible to say, but when we go to the beach all together (my city is near the cost, and we often go) I watch my best friend and I get triggered by her. I am so afraid to get a body like her. I just can't eat in those situations, and I know others notice and think I just do that for attention. I know I am very rude and probably I am not even a good friend, but I can't not spiral (I have never told her any of this nor commented on her body, obviously). I just feel horrible. Additionally, I have lost some weight recently because of stress and all above, and people started to compliment me. I feel so bad, because it does mean that I was repellent before.

Also, I feel completely alone most of the time. Many of my friends and some relatives too are in therapy. It feels so strange because I know I might need it but I can't afford it and nobody knows I struggle. I don't know what to do with myself.

(Sorry for the vent and for eventual typos, English is not my first language)