Cheating Hubby...What should I do?

Back in July, hubby and I were fighting alot, so I took our son and told him i was going to my sister's for the night...He took me up there and left. Instead of worrying about whether or not I was ever going to come home...he went and got some friends together to get drunk...one of his friends brought his sister (whom has always wanted my hubby) and sheflirted with him until she finally got him to sleep with her (in my bed!) He came and got me the next day and had a hickey mark but told me that it was from wrestling with his guy friend...A month later I found out by eavesdropping what had really happened that night. i left him again but went home after 3 days...as I have no income and I my son can't be dragged from place to place like that....He says he is genuinely sorry and that he never wants to hurt me again....but he has never acted like he truly regretted it..More like he got away with it...Its like he was able to cheat, get caught, get in trouble, and still have me and our son. I don't like the man he has become in the 4 years we have been married...I don't think this really qualifies as a question...I guess I'm just looking for advice...I can't leave because I have no means to support my son and I sure as hell aint letting hubby have him...I can't drive either...never really learned, plus I have no car...I have no where to go...Help me please...Share your cheating spouse stories or anything that might help me be less miserable....I do plan to leave BTW soon as I complete nursing school. I just need to know how to deal with him and his neglect until then.