Trapped in a relationship

Hi. I’m 17 years old, male, junior in high school. I’ve been dating my girlfriend for a year and a half now. We started dating about a month after I had my heart broken by a different girl. I was not ready for the relationship and did not think it through, but just jumped in. Now we’ve gone a long way; she is completely in love with me and I am wishing I could get out of the relationship. I have told her that I am completely committed to her, we are looking at the same colleges, we have given each other our virginities, etc. She wants to get married eventually and have a family, and I have reinforced this idea, which I deeply regret. I feel totally trapped. We initially began dating because I was in pain and foolishly jumped into a relationship, and it has spiraled out of control. We do not agree about anything in terms of religion, politics, etc. and I feel like we’re not compatible. However, I’ve not told her this, I’ve just told her that I want to be with her forever. I want to break up, but I am so scared. She is completely dependent on me. She tells me how much she needs me and how much she loves me every day. I love her so much, and I don’t want to hurt her, so I’ve gone along with everything. But the stress of it has caused me a spiral of depression and anxiety. I want to break up, but I know that if I do, she will either a) become terribly depressed, maybe kill herself, or b) get super angry, hate me forever. I cannot stand the thought of this. I also cannot bear this relationship. Please help.