I guess I do not need advice so much as approval or disapproval. I have been dating my girlfriend for almost 2 years. She and her 4 year old daughter moved in with me about 8 months ago, which was both a mistake and a revealing necessity. Immediately after we moved in, things changed. She was suddenly sick constantly and her job, out of nowhere became so stressful that she could barely handle it. Thinking it was probably a phase, I did everything to be as supportive, helpful and patient as I could. 8 months and 2 jobs for her later, things are the same. She never helps with chores or cleaning. Her financial contribution is minimal (due to switching to a less lucrative job) she cries or complains constantly about everything and has taken a back seat role in parenting her daughter. Her daughter, whom I loved growing close with and parenting as if she was my own, now resents me because she sees me as the guy who makes her do her chores, eat her dinner and go to bed and her mom is the fun one she rarely gets attention from. Bringing these things up with her, is admittedly hard because I am not a confrontational person and she responds terribly every time I bring them up.
The girlfriend now gets upset if she feels I slacked in any way in regards to her daughters upkeep (maybe I let a bath slip a day longer than it should because, you know, I am dealing with a lot here). She wants to diet but keeping her on track with that idea falls all on me. She hates when I spend time with my friends. She has karate's classes 4 nights a week which leaves me chained at home with her daughter with very little social interaction. She nags me about a marriage commitment constantly. She bought a wedding dress a few months ago as a "surprise", though I never proposed and had only really discussed marriage before moving in. She is always angry that I never want sex (I am mostly just exhausted with a full time plus job, child rearing, house cleaning, cooking, laundry and everything else) and is constantly nagging me about that.
I know it must end but I feel incredibly guilty about it. If it was just me and the girlfriend, I'd end it no problem. My reservations lie in the fact that I know her daughter will be heart broken. She is 5 and she sees me as her father ( her birth father is off at school somewhere and sees her maybe once every 6 months claiming he us going to come " save her" when he finishes school sometime in the next 3 to 6 years) I know that if it were not for me, she would be somewhat neglected. I know without me, they would have to move back with my girlfriends mom. I need the relationship to end, I am burnt out and unhappy but I feel irresponsible about ending it. I feel like a parent abandoning their child, even though she has started treating me like a brat and fights me on everything because she resents me.
Am I scum for leaving? Does it make me an irresponsible A-hole? What if I ruin the that child's life (or reduce her quality of life) by leaving for my own selfish reasons?