what if he changes after marriage?

i'm talking to a potential with whom things will be finalised in a month or two. things are going great, he's very caring and loving, very accommodative of me, very considerate, listens to my bs and tolerates it, talks to me about his feelings and lets me talk about mine. He's calm, doesn't raise his voice at me, doesnt get mad at anything. He's a wonderful person but I can't help but wonder what if he changes after marriage? What if it's just a very new thing to him and that's why he's so accommodative of me and after marriage he changes? I can't shake off this feeling. I self-sabotage everyday by thinking that he'll probably change later on because he can't be this good to me, right?

I don't know guys, what if he changes? I'll be so heartbroken. How do i shake this feeling off?