Help he kinda cheated

So my fiance had 3 kids. In there eyes I'm there mom because there "real" mom left them for drugs, well him and his baby mamma have been texting and calling each other. He denied it but I got pictures sent to me of him asking for nudes. He proposed to me and were ttc. He proves he loves me every day. He cry's on the thought of me leaving and tells me he can't live without me..he means the world to me along with his 3 kids. They call me mom. He brings me happiness..he went to jail tonight and I stayed with the kids. His baby mamma sent me the nudes and pictures of him that he sent her..I'm broken I love him with everything I have..I'm marrying him! I know he loves me..if he stops talking to his baby mamma and proves he loves me should i give him another chance.. I know he loves me. IDK why he did that. If he gets out today I'm going to talk to him about it and show him the proof. I have one of the pictures of him without a shirt on as my wallpaper on my phone to see if he notices..I don't want to leave him because he means the world to me..I'm lost without him. What should I do ladies. Help me please I'm so confused. He's an amazing guy..and I know he loves me...