Mistake...

So my ex and I have been broken up for approximately 3 weeks. Right after we broke up he started talking to a new girl. I don't know what happened but they are no longer talking and she blocked him. Anyway, since then he's been calling me nonstop again. At first he came to me crying telling me he wanted to see the kids but had nowhere to take them because he was homeless, and asked if he could come spend time with them at my house. I agreed because my kids love spending time with their dad. That turned into him asking to sleep over and eventually asking me if he could move into my guest room and pay rent. At first I said no but eventually felt bad for him and agreed. He's also been trying to guilt trip me telling me that my kids will suffer because their parents aren't together and that he would never allow me to be happy with anyone else. Then he would constantly say things like that I didn't realize what I had standing right in front of me and how he would tell his kids how I never loved him when they got older and asked why we weren't together. This made me upset and made me feel guilty but even more confused because he was the one that made the choice to break up with me. He reasoning for leaving was that I was doing enough to help him get out of his current situation which was him being homeless. So after a few days he began to act distant again. He would still text me telling me lies that he was going to jail for a really long time and that I would no longer see him. He would call the next morning laughing and telling me he only told me that because he knew I didn't care about him. So he basically made me worry just to get a reaction out of me. So today I mentioned possibly getting back together because I felt horrible of the way he always made me feel bad about not being with him. His response was completely different and he told me he wouldn't be with me unless I showed him I was 100% dedicated to him and did what he needed to be done. So what was all that guilt tripping for? Just to tell me I had to work to be with him? The confusion is so frustrating and depressing. To top it off I found out that he's talking to another girl. This time is horrible because a few years ago I was pregnant with my son and he claimed to not be pursuing this girl even though I knew he was. Now I know for sure he had something going on because their talking again. I feel completely betrayed because after I showed him kindness and allowed him to come into my house he slaps me in the face. Then tells me I'm crazy because just because he's talking to her doesn't mean he's with her. Which I know he's lying because he says that about every girl he's messing with. I don't know why I started talking to him again bit I feel like I got hurt all over again...