Why is it so hard ?

I want to leave my bf for good! But why is it so freaking hard ? I hate these feelings so much. He is the father of my children and we have been together for 4 years but I'm fed up mentally unfortunately im not fed up emotionally it seems because every time he messes up I take him back. He has hit me numerous times including while I was pregnant both times he has cheated idk about physically but I've for sure caught him I swear about 20 times messaging women creating secret emails sending and receiving naked pictures. When I was in labor with our daughter he even was messaging girls and getting naked pics from them. He was telling them he loved them and wanted them to have his baby all while I was in labor!!! He has pulled knives on me when he thought I was cheating but why am I so stupid? Why is my heart w this person who I know is no good? What can help my feelings stop. Every time I leave he begs me so hard makes me feel bad for him. He's like "you don't give up on love" has anyone been through this? like what do I freakinh do im losing my mind. I want these feelings gone!!!!!!! Please help and thank you