Relationship trouble

I was married for 30 years and now single for 12 years. I am dating someone for the past 7 years, but it is up down up down all the way. He is a difficult person to the extend that whatever I do, I am called stupid etc. We got engaged a couple of months back, then I discovered he is seeing others behind my back. He claimed it is work related, but the smse shows a different story. My problem is, I find it hard to leave him. Even now I told him I am done. I need to know how to go about it as I always take him back.

No group. I am by myself. It is just so overwhelming, you know. I dont know why he changes like this. Then he is a different person. he claims it is workstress, but I do not know. I moved in with him and the very same minute he was chatting up another. I phoned all those girls. They never knew we were engaged let alone together. He told them he was single. The next day while he was at work, I moved out. So now, he wont let me go. And now, I am given the usual SILENT TREATMENT for days again

I fail to not see the good in him and my kids absolutely wants me to leave him once and for all. But he DID change lately, I just dont know why he acts like this sometimes. I forgave him but maybe that was a mistake? I know I must very soon make a final decision, I just wish I knew how to go about it.