Hubby texted his ex behind my back what should i do

I saw a text that my hubby text a girl and in that text it seemed like she didn’t want to talk to him but he kept on insisting her to. I learned that he even sent her money. I confronted him, he said that he dated her a long time ago and recently she needs help w financial so he sent her some money to help her out. She lives 6 hrs away from him. He said he did not see her bc he always home w me n my son. I’m very mad st him right now n i told him i want to divorce him. He begged me not to n said he’s stupid n pls forgive him. I don’t know what to do! Our son is only 7m old. Would you gal be able to forgive someone for that? Is this a form of cheating?