Should I stay or should I go?

My current boyfriend on and off for 3 years now each time I broke it off, while on a nine month"break" ( we were still having unprotected sex every other weekend like we have since we met) had sex with two other girls. One girl he slept with for awhile because she began growing feelings and wanted a relationship. When he refused she was upset and they stop seeing each other. I was at work one day and received a text from the girl stating she was pregnant and I was pregnant as will, which is why she felt the need to tell me. He lied and told her I was pregnant thinking she would follow through with the abortion so he said they already discussed. I called her to confirm she said they hadn't seen each other in a month or so and she wanted nothing to do with him but told me she was considering keeping the baby. She ended up having the abortion due to her religion background and strict parents ( If she was really pregnant). I've been through a similar situation in a previous relationship and when I forgave him he was still seeing the other girl (a friend of the girl I'm in this situation with now) and I just don't want to play the foul again. Any advice? We were suppose to have a family already but I had an abortion because I wasn't ready to be a parent at 19 two years ago but as I'm getting older I'm realizing I may have pushed him away. He's never done anything like this before and I dont know if the behavior will continue but I don't want to look to and find out it will