I don't know what to do.

I'm with the love of my life and we discussed many times that we need to be careful with our sex life but then, I missed a period. I can't go through with it and as amazing as he is, he wants to go through with it and is ready. He admits he's scared but excited. I don't know if I am. I've never felt excited. I feel heartless and I don't want to lose him. I can't lose him. I feel that I have to go through with this to keep him in my life. He said he'll still love me but he'll be hurt. I know I'm incredibly lucky to have someone who is willing to support me. I'm not ready to change my life. I was only ready for him and I. Everyone's situation is different.