How do I leave the guy that im in love with?

Alright, I’ve known this guy for a really long time, we grew up together. I have always had a thing for him and we ended up dating, well at first he was so sweet and treated me really good. Of course it was to good to be true. I have always heard things about him that he was pretty much uhh well he got around a lot and well he has been around a lot but I over looked it we both went and got tested and everything was fine. We were really happy together but then people started telling me that they seen him out with other females but I over looked it because they werent very good sources, but now im starting to believe that because he barley has time to even talk to me anymore and he’s always “at work” yeah well I believe he’s seeing another woman. He also doesnt treat me like he used to his gentlemen side disapeared, and it seems like this disapeared and he started changing once we were engaged im starting to think that he is getting cold feet or just doesnt want to marry me anymore but everytime I try to talk about it he just tells me that he still does and that he loves me very much. He is showing the exact opposite of that though.Every time I try to leave he reals me back in, I have never had a problem leaving a guy before but with him its so hard, its like im not strong enough anymore. Help! I cant marry someone who treats me like this!