I'm screwed

Been married for 5 years and it's been ok. My husband used to like to drink occasionally and that's fine but recently it's turned into an everyday, multiple drink (hard liquor) thing and he just sits and plays video games all day. He doesn't help clean the house, cook or do anything an adult should do. He never wants to do anything outside and I miss time that we used to spend together. I mentioned to him on a few occasions I feel abandoned and he laughed it off. I asked for counseling and he said no way. I ended up sleeping with my best friend just once and didn't think about how I was around ovulation. Fast forward months later, I'm pregnant.  5 months pregnant. Deep down inside I believe it's my friends. My husband and I tried for years to conceive to no avail. As I get closer to delivery, I keep telling myself I need to let my husband know what I've done but I can't bring myself to do it. I've even thought about not saying anything at all and just go along with everything like normal... Sigh. Thoughts?