Do i need him in my life?

have been in a relationship with my fiance for 4 1/2 years now. We have 2 children together under 3 and I have 2 older children from a prior relationship, also he has 2 other children that live in another country. My problem is we separated for a few months while i was pregnant with our youngest and he started a relationship with someone else.. He never told me about her and was having unprotected sex with the both of us while I was pregnant. We got back together and It has been a nightmare ever since. He did not end the relationship with her and physically, verbally and emotionally abused me to the max.. Calling me names, complaining about my body. He has humilliated me so much and put this other woman before his own family. Not worrying about our health,safety and well being. All this has been going on for a year now.. the lies and deceit. He turned into a complete monster. The worst monster ever. I am a christian woman and have tried to work it out for the sake of the kids. The other woman and him would make fun of me for this telling me that as long as he was home i should be happy because I have my family. My mind is screwed up so badly that I have nightmares, paranoia, anxiety and a lot of depression. I have cried everyday for the past year and the pain does not seem to be getting better. Along with all of this came his impotence.. he has trouble each and everytime. As of 3 months ago, he has been acting differently, nicer, sweeter and is talking more with me though he has trouble talking about the more with me though he has trouble talking about the affair. He says that as of February he has no contact with that woman and that he wants to focus on his family and making things better. He has always blamed me for EVERYTHING and though he has apologized for everything and given me a bit of detail of what was going on in his mind during the affair he now blames me for his impotence. He says because of me not being over it he worries about what I am thinking and cannot perform. I feel used, abused, humilliated, not sexy, not a woman. I am at the breaking point and even have thought about cheating on him but i know i could not do it. I pray and ask God for his guidance in my life. I am at the middle of a storm and I dont know how to get out of it. I dont trust him, I dont want him to touch me sometimes. When he is nice i wonder why and I am always ready for something bad to happen. I am seriously thinking about leaving but I paralyze at the thought of my kids not having their dad. They are crazy about him. I need advice, some hope, some enlightenment because I am truly truly lost and devastated.