15, and VERY confused

Guys I need your help.Sorry for potential bad grammar/spelling, English is not my first language and I'm having trouble writing down how I feel. Also my formatting will be kinda bad, I just don't know how to write all of this down properly.Im 15, Male. Ive had crushes on girls before, not a lot though. I also never had a girlfriend/boyfriend. A few years ago I realised some guys looked pretty good, I got scared, thought I was gay/bi etc. That period didn't last long though, I kinda forgot about it for 2 years.Ive never had anything against LGBT people, my family doesnt either and I have gay, bi and trans friends.So since a couple of months ago, I got a lot of new friends, including some guys that I now hang out with very regularly. It started with 2 friends who have a huge bromance making some jokes about "a little gay is okay", which I found appealing, I started thinking about experimenting with them.A couple of months and lots of masturbation (mostly gay, some straight) later I met this pretty good loking guy, we are now good friends.However in last couple of days he and I started doing some VERY subtle flirting, at first it turned me on, A LOT. However after I noticed some "less subtle" advances from him I got seriously creeped out felt and EXTREMELY uncomfortable. I didn't want to do anything with him and kinda avoided him for the rest of the day.Now my problema are:A. I don't know if im secretly very afraid of being bi, or if I'm really not that into guys.B. I like girls, For example there is this girl who I had a crush on, (but found out that she didnt have a crush on me) she very nice, cute and funny and I felt 100% comfortable with her, I would have loved to have her as my girlfriend. But I never masturbated thinking of her, I just found it innapropriate because I knew she was not interested in sex whatsoever (I'm in a very high level education school, most girls arent haveing sex yet while in lower education guys/girls are).Guys however, I don't like too much, my friends are 50/50 F/M and I have never had a "crush" on a guy, I was only interested in sexual experimentation (also I really cant see myself in a relationship with a guy, just no.). However I cant stop masturbating to gay porn and thinking of guys, While Im having trouble masturbating to straight porn and loads of trouble masturbating to lesbian porn. Its just that taboo feeling that turns me on so much.What can I so to figure out my sexuality? I am planning on completely stopping the subtle flirting with this "straight" guy because I think it would ruin our friendship.TL;DR Girls? Love em, cute, funny, nice, don't care about looks too much though. Also having trouble masturbating to girls, it feels inappropriate.Guys? Gay porn? Thats some taboo ish stuff and turns me on a lot, I can easily masturbate thinking of guys, also I don't feel bad because I know they do too, but being in an actual relationship with a guy? Hell no. (Not because Im afraid of negative responses, but because I just really cant see myself in a romantic relationship with a guy.)