What does it mean if he does this?

My boyfriend and I have been together for a year and we ended up moving in together about 3 months ago. He’s 31 and I’m 25. I’ve noticed that sometimes he will be so loving and caring and basically seem “all in” he tells me he wants to marry me and stuff but once I’m loving and stuff with him he gets distant and quiet. I mean, I’m always loving and caring but I feel like if he is, then I have to pretend not to like it or he will stop. I’m just really confused on why he seems to get distant and act like he’s basically kind of better than me or to good for me after he was being cute and sweet. Has this happened to anyone else?