is it obvious?😔

I have been married for 8 years 7 months. My husband and I have 3 beautiful kids the youngest is only 2 months old, the older ones are 6&7. I found out he had a one night stand back in 2014 and the girl is claiming her one year old daughter is his. I deleted my Facebook because this girl and her mom were going on my page taking pictures of my kids and making side-by-side collages of them and the little girl to compare and say that the little girl looks just like my kids 😡 when I found out he cheated we split up and with time (only 2 months later) I decided to let him come home and work things out, everything was fine even though the trust is not the same and I might never be truly over it, but now it's not just he cheated, now there's this kid and I just don't know if I can live with not knowing if he has a child with someone else or not. I guess I just need to hear some advice from some people who aren't biased. My family thinks I should leave him obviously and his is trying to convince me that the child is not his and this girl is jus trying to mess with our marriage. This happened in Puerto Rico and we moved to Oklahoma about a year ago. How should I deal with this?i can't even look at him right now I'm so mad and hurt and confused.😔😔 please, just someone tell me something 😔