In love with two people: what should I do?

I've been in a relationship with someone since the end of 7th grade and I'm in 10th grade now and I met this guy in 11th grade and we became friends and eventually I developed a crush if sorts on this guy and I told him about it and he said he liked me back so I asked my boyfriend if maybe we could have a poly relationship and before I could even explain why I wanted to know or who the other person was he got upset with me and said no. Which I respect and all but I've liked this other guy for like 4 months now and my boyfriend says I don't actually like he's basically saying I'm dillusional about liking this other guy but I really like this other guy and want to be with him because of how good he makes me feel but I also want to stay with my boyfriend because we promised each other we wouldn't leave especially not for another person but I'm starting to doubt everything I thought I knew. I always said I. would never leave but at this point I'm thinking it may be better for me and it doesn't help that my boyfriend constantly asks for sex and he claims I'm more than just sex to him but lately that's almost all he seems to care about. If I talk about the guy I like he gets upset and says I probably don't like him because my boyfriend says that just because he only has feelings for me and no one else I can't have feelings for someone else. And I know having feelings for someone else while in a relationship is a common thing it makes me sad that I can't date the other guy I like because I love both of them very much and don't wanna hurt either of them but lately I've been seeing a new side to my boyfriend that I don't really like and it all makes me wonder if I should've just kept my mouth shut about everything and just suffered through it all. I just really don't know what to do I love them both and I just wish to have them both. Any and all advice is appreciated