How do I get my fiancé to stop cheating?

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My fiancé and I have been engaged for a year now. I run or household. I buy him cigarettes I give him whatever he wants. Well, I recently found out that he has another woman at work that has been giving him money as well. I found out about that and cussed that woman out on facebook. Then, I found messages in his phone where he was talking to a really young girl. Apparently he had given this young girl a ring and told tried to get her pregnant numerous time. She texted him and said "What if I'm pregnant" and he said "I would be happy I love you a lot baby" They then started talking about having sex again so she could try to get pregnant again. I KNOW he loves me. I think he is just using this young girl. How do I get him to sop cheating and want me again? Please help me?
He is cheating with two women btw. The older woman(who gives him money) and the younger one.