HELP! Single man crazy over me

I have a friend who's also my coworker, and hes single. However, im married and have 5 kids. But he will not leave me alone at all. I have told him that i will not leave my husband for him, but he said if he has to die to get me, he will. He said no matter what, he will never stop pursuing me.

Ive told him plenty of times, no. So one time, i decided to cut all ties and contact with him. He was very sad, came up to me at work, and told me to stop it. He said he wants to be there for me, even if he has to wait til hes old, he will always be there to wait for me to leave my husband. I told him i never will though, and he said as long as he knows he tried his all to get me to be his. But he said he will never stop trying to get me to be his, even if it takes his life away. He said theres nothing on earth for him, but me. And one time he even talked about the next life of getting me to be his.

Im a bit scared about it, idk what to do. I feel like he might do something crazy to me. Or even my family. Like what if he kills me and himself? Idk.. what should i do?