Advice?

I’ve been talking to this guy for a year now. But we’re “getting to know each other” I’m completely exclusive to him, but I Knowhe “talks” to other girls. I became super close to him and things were good. We ended up having a vacation together. But he started acting different one day to the next. I spent the night, like usual, at his place and he’s been so distant since the day after. He barely replies and when he does it’s short and quick.

I don’t know what to do. I don’t know what to think or feel at the moment.