Am I Bi?

Anonymous
So, here's the deal: I've been attracted to both males and females since I've started having sexual attraction towards people and have identified with that label since I was 13. Well, I'm turning 17 now, and my boyfriend is telling me that he's pretty sure that I've just convinced myself I'm bisexual because all my friends are in the LGBTQ+ community. A part of me wants to call complete bull, but another part of me wonders if he's right, although I don't know why. Long story short, I told him I would stop going around and telling people I was bi.
It should be noted that when ever I brought up my bisexuality, he would always counter it with the fact that I'm in a straight monogamous relationship with him and that due to this, I was now straight. Whenever I tried to tell him otherwise he wouldn't listen.
So, did I just convince myself that I'm bi or what?