Soon to be husband cheated with ex wife. We are both pregnant.

Messy right? He cheated on me early in our relationship, when I was about 13 weeks pregnant. Well I forgave him. Divorces are messy and she's a manipulative piece of work. (They were legally divorced two weeks later) This is not about that. She has recently come out that she is pregnant. I have seen ultrasounds and she most definitely is. We don't know if its his as she was engaged to someone else at the time as well, and was seeing a third man. She hates us together and constantly calls and texts about how he doesn't care that she is pregnant with his son because his whore (me) is pregnant too. Most of me doesn't think it's his. But of course we will not know until the baby is born. We are getting married next week. Everything has been paid for. I feel really overwhelmed. I do love this man. But what if it's his? I don't know if I'm looking for advice or just to vent. This has all been very hard on me. :( oh if anyone wants to take a gander she is due September 14th and their only date of intercourse was January 10th. Please don't be rude. I literally have no one to talk to.