Planning on divorce but I'm not 100% sure it's the right choice... Help?

My husband and I have been together since 2008, had our first baby in 2010 when I was 16 and he was 19. Got married in 2013. Last year around October, I found out that he was communicating with his ex girlfriend who lives in another state. I found out he had a secret email account where they first started communicating bc there's messages between the 2. And a picture of her so I knew which ex it was, the same one he broke up with me for when we first started dating. And on top of that I found out that he was into the whole webcam thing, paying for these 5-10+ min shows. I went onto his "webcam" history bc they email him his "receipts" totaling to almost $300+. And I also looked at his old card statements from years ago and noticed that this has been going on for a while, probably since before/after we got married. I confronted him about this and his ex gf and looked up his call logs online and noticed that they would talk on the phone for 30+ mins texting too, going on for 3+ months. He told me he stopped talking to her bc he felt bad. Fast forward to now and our relationship hasn't been the same. We are still sexually active but other than that, I distance myself from him. Our only child started school this week, and I'm not sure if I want a divorce right now. I haven't worked since 2012, he's been maintaining me since, I am a SAHM. I'm scared of divorce but I feel like it's something I have to do, but don't really want to bc I fear change. I don't want to change our child's lifestyle, I'm scared of the whole co-parenting thing. I am unhappy in our marriage and I know he is too. I talked to him about divorce last year but he refused. But why does he want to keep me when he knows were unhappy?