I want to lose the sense of bitterness

Back in october I broke up with my girlfriend after finding out she had cheated multiple times with different men. I was finally starting to get my head back together and now I have found out she was pregnant and had an abortion just two weeks ago. The timing means that the baby was most likely mine, I have gained back all the bitterness and anger that I thought I managed to shake off, but it's worse now with a sense of extreme sadness at the loss of a little girl and extra anger that she didn't even tell me whilst we were still together that she was pregnant, despite me even suspecting it at one point and asking her, she said she wasn't. She often used to say what a great dad i would make and that she wanted children with me, then when one finally comes along she doesn't tell me, cheats and then waits until she's 6 months pregnant to abort, having already spent several nights a week in that time drunk out of her mind anyway. If anybody has been in a similar situation then please give me some tips on getting over this, I have been lied to and messed around for over 2 years and this is doing me no good at all.