My husband lives with his mistressand our kids and her kids

My husband and I have been together for 7years married for 2years. We have 3 kids. After we got married I left him after 3 months because on the week of our honeymoon, he asked a couple to go into our hotel room, knowing our history I knew wat was to possibly happen. They said no thank God. I warned him I was not going back to our old days of swinging. We only did that a handful of times. Then afterwards, he asks me if I want to go to a stripper club! So I left him for 1 yr. He kept begging me back and I regret not taking him back because he found himself a girlfriend. He then moved her in to his house. He has been with her for a year. He began to pursue me meanwhile and I finally gave in to his pleading. And when I did, he completely switched on me by arguing that “why now” do I decide to go back to him. It almost sounded like he was choosing to stay with his lover. A few months have passed and he is still with her saying that she is moving out and since she doesn’t have a job she can’t leave. My children say they call each love names and sleep together in the same room again (she was staying in the living room so that he wouldn’t have sex with her) …am I guilty for leaving? Do I deserve what is going on? He said he was going to give me the divorce not because of her but for other reasons. Although he is still sending me pics of us and sending me small hints that im still on his mind. My oldest son tells me he resents me for leaving in the first place. I am an emotional miserable person walking on Earth. What is the reality of this situation?