Why am I crying when this is what I want?

It hurts so bad because it is an ending with someone that you've had a personal relationship with.  I agree with M in that occasional sex was not a good idea .  It still keeps you in the relationship physically and emotionally, which is what you are experiencing now.  When we begin to feel that empty void is when we really begin missing those phone calls, the occasional physical intimacy, quick dinners, etc.  But do not forget who he really is.  Someone who has a past of being abusive that could potentially become much worse and dangerous to you and your children.  You have recognized it yourself, h he is "no good" to you.  Protect yourself and your children,  the less contact you have with him, the better off you are.  The pain will pass in time.