Husband wants his cake and eat it to.

I've been married to my husband for 12 years and during this time both of us have been active duty Navy.  My husband was deployed to Iraq back in 2005 and during this time he started having an affair with another member. At first he said he believed that he wanted a new start in life, that he loved her, and she felt that they were just meant to be together.  I guess you can say everything was good for him until he had to come back to Japan (we were stationed here at the time) & she went back to the states.  When he got back & told me, we seperated and I started divorce proceedings.  Within 6 months, he started doubting everything and convinced me to try again because he believed that he had the affair because of all the things that were happening in Iraq and he needed something to make him feel human or better.  We went to counseling and everything started to get better.  Last year we transferred back to the states in Jan, bought a house, and things were good.  In Aug, that same girl from Iraq transferred not only to the same base as us, but the same command as my husband and yes she wanted to start things back up. I guess I should tell you that I'm 34, my husband 33, and this other woman is 25 probably every guys mid-life fantasy.  Anyway my husband fell for the bull**** that this was fate bringing them back together and everything and started having an affair.  For the first couple of months, I believed him that nothing was going on but then in Nov she called me to inform me not only were they sleeping together but when they started.  At this point, I couldn't deny it anymore.  I sat down with my husband and told him that I wanted a seperation and tried to understand why.  He did his thing of were he tried, said he was sorry, and I was what he wanted and promised he would stop.  This same conversation happen 3, 4 times & he just kept having the affair.  I have finally taking my children & moved away because I couldn't take it any longer.  I had asked him to leave but he would just show up when he wanted and I couldn't get past it or try to heal not to mention that his other woman that he was staying with lived 2 min from my house.  I could literally look out my bathroom window & see her apartment.  I was driving myself crazy so I felt I had to leave.  Now my boys & I are having to stay with my parents until I find something while he is in our house letting her enjoy exactly what she had wanted all a long.  She wanted my life and she down has it.  The only problem is my husband keeps telling me that he thinks this is temporary that he doesnt care for her anymore, and that we are suppose to be together.  I don't know why but I still love him.  I keep making the decision that its over, but then I start worrying if I'm making the wrong decision.  I  don't understand.  I'm the one having to start over while he is still going out with her, having her in my home, and who knows what.  Why do I still care?  Why can't I just walk away from him? Why do I care if she gets what she wants?  Because honestly I don't think she will, I think my husband when he finally realizes that he lost his family, will hate her.  I don't understand how people like her get what they want.  My husband is the 3rd married man that she has had an affair with, or I guess you can say the 4th seeing as this is the second time around for them.  She doesn't care who she hurts as long as she gets what she wants.  I considered myself a good person so why am I the one hurting.  I'm so confused.