Help breaking it off with someone

Hello all, this may seem kinda stupid but I was wondering what the best way to end things with someone without any major problems?

To properly preference this he’s very nice and caring though there’s just this itch I can’t seem to get past it. I’m trying to end things with him as it’s definitely not really working for me but not really too sure how to go about doing it. I was stationed in Korea in February and met him a few months after arriving here and things started pretty good but now it seems to give me like stocker ish vibes and when he drinks he is a completely different person and not really in the best way.