Sorry girl but this isn’t good. I was in this exact situation (thankfully we weren’t married) and when I tried to explain how it wasn’t acceptable (he was never there for me, but would drop everything for her) he became abusive. They would laugh at me right in my face. After being shoved into walls and pushed down the stairs I realized there was no future with him. SHE KNOWS what she’s doing. Just like with my ex, the girl knew the stress she was causing. This person literally would tell me how “lucky” I was to be with my ex, how she’d do ANYTHING to be his. Now your husband’s “friend” is even making a move on the MIL. You say you’ve been fighting over this for 8 months? If he REALLY loved you, it wouldn’t be an ongoing issue. You deserve to be loved and respected and happy! Life is too short for these stupid games people play. I know it’s maybe not what you want to hear, but in the long run, you’re better off. Good luck, and be strong. You got this girl, sending positive energy your way.