ADVICE PLEASE HELP

Me & my boyfriend have been together for 8 months now & we just started building our life together, at the beginning of our relationship his ex found out she was pregnant BUT she didn’t know for sure if the baby was his. The baby was just born Sunday and looks JUST like him I’m devastated and beyond hurt. This girl is in love with him & she’s crazy literally for example telling him his dead mother sent her this baby. I don’t know what to do he wants to be a part of this child’s life if the baby is his which I know she is but we are waiting on DNA results before we do anything else. Me & this girl DO NOT get along & probably never will. Advice? Thoughts? I just need someone to tell me what to do or what you would do In this situation but leaving him is not a option I’m so in love with him.