ROMANCE!! I Once Had Sex With Another Girl And Now My Boyfriend Keeps Asking To Have A Threesome

I have decided to write to you about my own situation because I have no clue on what I should do.
My boyfriend and I have been together for 7 years. We have a 7 year old daughter together and in about a
month I’ll be having our son.
When our daughter was about 9 months, we decided to really be a family. Everything was going perfect, meaning he was working and taking excellent care of me and our daughter. Neither of us wanted for anything at all. I was in school and he constantly worked to support us.

Fast forward to last year, 2012. We had been in our own place for about 6 months and I had sex with another female. I told him about it almost 2 weeks later because I didn’t want to hide it anymore. He told me he felt as though I owed him a threesome because of this. I told him it wasn’t happening because I can’t bring myself to watch him have sex with another woman in my face. He basically made me feel like if I didn’t give it to him, he would leave me.

I thought nothing of it because I felt as though if you’re gonna make me do this, it’s out of revenge and not for fun. He kept bringing up the fact that it wasn’t fair for me to be able to sleep with someone else and he couldn’t. I kept reinforcing that it wasn’t gonna happen and we were basically preparing to break up.

A couple months went by and I found out I was pregnant. We decided to keep the baby, but in the beginning he has made this pregnancy a living Hell. He constantly gets angry at me. One minute he’s all in love and the next minute he says the most hurtful things to me. He claims it’s because I’ve never made up to him for what I’ve done.

I try to be open to the situation because I do feel like I messed up, but at the same time it feels like revenge to me. I’m unsure if I should do this because he had said some really mean and nasty things to me over the past year, but at the end of the day he comes home and kisses me and says how he was just angry and he really does love me. But, I get to the point where I feel like when I have my son, I want to move on because I feel like a threesome would further complicate things and make me resent him.

I’m also scared that if I was to put my pride aside and do this threesome for him, I would begin to cheat to get my version of revenge, which isn’t good. My family all like him and keep questioning him about when he’s gonna marry me. He just laughs it off and when we’re alone he reiterates to me that until I make something happen, I won’t be getting a ring.

Honestly at this point, I don’t want one because I can’t see myself being married to someone who has emotionally drained me for so long because of my past. The freaky side of me wants to do this threesome and throw caution to the wind just to have fun but the other side of me keeps thinking what if I get into the situation and don’t like it? What if I end up getting hurt behind it? Please give me some advice.