Confussed, hurt and pregnant

I Have been split up from my boyfriend of 5 years for about 3 months now. We have been seeing each other on and off during this 3 months because we still love each other and we have a mortgage together. Last week i found out he met someone during this 3 month split on the internet and she is now claiming she is pregnant. They don't know each other and have only met twice. since then i have also found out i'm pregnant. It is really hard for me as i should be looking after myself at the moment as i had a miscarriage a year ago. I should be enjoying the pregnancy but instead i'm hurt, upset and confussed. i really do love this man and i feel i can get over the sleeping with someone whilst we had split up but i don't know if i can carry on knowing she is having his baby. he really does not want anything to do with this other woman and wants my forgiveness so we can be together again. WHAT SHOULD I DO???? please all advise welcome. thanks