I don’t know what this means

So I’ve been in a relationship for 2 years. We’ve had a good relationship but there obviously has been things that have happened. he’s always shown me affection and patience. Lately I’ve been feeling disconnected from him and that I don’t want to spend time with him as much. I don’t initiate sex, and when he does I often turn him down. We barely kiss, hold hands or say I love you anymore, but that is mainly coming from me. He’ll try to kiss me and I’ll move away. I’m not sure why I do but I’ve just been feeling like I want to be alone and that we don’t have a future (even though we’ve always talked about getting married). Why am I feeling like this?