I had a very simular situation with a Sag, he is the father of my child, and for the whole of the pregnancy would tell me I was beautiful, that he loved me then he would cheat and treat me no better than a piece of crap his shoe, verbally and psyhically abusive...He would make me feel as I was treading on egg shells...
He put me in such a position that when I went into labour I was scared to tell him - incase he was doing something more important, (needless to say he fucked off to the other side of the world, I found out of his family when I was in hospital)
I look back now and think I was a fool....However he used to also be very insecure and although didn't care about me he would hate it if I got any other male attention.
I hope u find it in urself to come to terms that this cancer man seems a vile, maniulative bully and you can move on....you don't need someone jealous and possesive in your life....
The end of my story is that the sag wants me back and has completely changed his ways, he wants to be with me and our child but I know longer love him and were now good friends.