If i was in your situation. I have made two plans:
Plan A:
I'd get back with her, use her to f**k for roughly a week (week two). Talk About other people all the time, go riding all the time. Never text/call her back, arrange to do somthing and then text her 15 mins late saying sorry babe i cant make it today, dont give a reason. Be a general lazy person around her. Get mates and her over, but only talk to your mates, get 'hammered' and then start talking about other ex's and how much you miss them and how good they were. And so on. Aim to do this for two weeks.
Plan B: (quick skim reading not sure if shes pregs/the kid is yours)
Ring her, tell her that you dont belive the baby (?) is yours, shes a lieing cheating slag, you have got clap, your impotent due to the clap so the pregnancy can not be yours. you have proof that she is cheating on you. And then turn it 50% and say you still love her, but will never be with a cheat, and never a lier and so on.
Obviously im a Cword unt. So would use these if need be.
But they work . Well plan A does for me anyways.
All good, end of problem.