Starry sky is right. You do not have to marry him.
It sounds like you need a better Therapist. You might consider finding a support group somewhere.
I know you're in the thick of it now and it's very hard to see a way out I felt that way too. My partner wanted to get married too. We Argued about it about it often and I thought I was hurting her. So I thought I was the bad guy because I had reservations. I'm convinced myself that it was something I wanted too. I tried to be as honest as I could without starting fights. But it's hard to be totally honest when you feel like you're walking on eggshells. All that is understandable Trust your instincts. Trust your gut. You are not crazy. There are reasons you feel the way you do. Your Feelings matter just as much