From the "other side" (meaning, someone definitely old enough to be your mom):
What in the heck are you doing having sex at 15

Why are you in such a hurry to grow up? What will you have to look forward to

You've been extraordinarly fortunate that you haven't gotten pregnant, or you'd have one more problem on your plate.
You must understand that one doesn't "jump over the line" and back when one decides one is Gay. (Bisexuality is another matter). If he decides he's Gay, then you are out of the running. He may be trying to decide whether or not he is, and the only thing you can do is to give him space. Being needy and clinging right now is the surest way to get pushed away.
It appears that your relationship has taken a turn. Relationships are dynamic; they evolve over time. At least the good ones do. For you the relationship is in the process of finding a new center, one that you might not like. You have to decide what you want in this relationship. If it kills you that things aren't like they were and may never go back that way then I think you need to tell him so, in a non-accusatory way. You can't change what he is anymore than he can change you.
I've been extremely fortunate to have male friends in my life. Not ex-bfs, friends that happened to be male. I could go to them just I like I could go to any of my gfs whenever I had problems and vice versa. They were like brothers to me and I felt we were closer than any romantic relationship could be because we had been through so much together without any expectations. We accepted each other for who we are--if they had a gf I was thrilled for them.
I'm not certain while you're still going out even though there appears to be very little holding you together. I suspect it's because you're afraid to be on your own again and a "bad" relationship is better than none. I've gone on that ride before a few times. If you value him as a friend ONLY (and friendship evolves ofer time), then it's still win-win. The two of you can have a friendship that very few people have.
Otherwise, you're going have to let him know that you can't handle what's happening now and need time to think this over. You also have to define what you will and will not do with him. When I was in my 30s I was with this guy who was a born-again Christian. We would make out at his house and one thing would lead to another...and when things were over, he'd start lecturing me about scripture. I think he was trying to have it both ways. I started drawing a line and he'd say that was fine and it was...until he initiated things. Then it was the same old thing. After awhile I got tired of being pulled and pushed and, much as I hated to do it, I had to end it. I did and never looked back.
I know it's hard to not know what tomorrow will bring for the two of you but you must let things run their course. Your romantic relationship is non-exclusive so you are free to see whomever you want so go ahead.
But wait on the sex thing--that's the absolute worst thing to base a relationship on. That comes at the end.
Good luck and do keep posting.