Why can't I get this man out of my system?

I have a FWB for 3 years. We became very close. My personality is jealous and possessive and I speak my mind. However, I am loving, giving and sometimes over-sensitive. Sometimes i feel he takes me for granted because I have feelings for him and he knows when times get hard, I will not walk away from him and always be there. I have found out there is a child I knew nothing about (she was born before I met him) and he has alot of female Friends, most are women who were FWB's. Being the jealous person I am, I don't like that. I have tried to cut him off a few times before but end up missing him so much, i go back to him. He is there for me if I need anything, he is a generous person. He does not want to be in a relationship. There was a time that I loved him and wanted to be in a relationship with him but he is against it, so I continued with the FWB thing. I think about him all the time and feel compelled to always help him when he needs anything. I tried to deal with someone else but this person ended up being very stubborn and wanting to control everything. I just need to know how to end the FWB thing. Obviously, I have a weakness for this guy and can't walk away.