<human>: Can you succinctly summarize the text in 1-3 sentences?

First of all I would NEVER ask my boyfriend to choose between me and his daughter, let's get that out of the way. We have been living together for three months, Brandon and me. He was upfront about having a child from when we first started talking and I was slightly hesitant initially, but he told me he didn't even have custody, he hardly saw the kid, wanted to give her up for adoption, etc.... just, very negative things. I'm not a fan of children and I hate watching them, I let him know this from the start. Well, it turns out his kid is a bigger part then he let on and there have been several occasions when he had to watch her and I was roped in, as well. I was mildly irritated, but I really liked his kid! She's pretty awesome and seems to have taken to me, so no problems there. I don't want to get into the details of custody and the relationship with his ex because it would make this super long, but his ex is neglectful and apparently unstable, so now Brandon wants to fight for custody which is great, honestly, he really is a good father and his daughter deserves better than her shit mother, but... I didn't sign up for this. I'm not ready for the responsibility of a child. Brandon wants me to co-parent and already told his daughter that I'm her "step-mommy". What do I do in this position??? I don't want to break up because this sounds so horrible and selfish, but I don't think I can deal!
<bot>: Boyfriend is fighting for custody of his two year old custody, wants me to play step-mom, I don't want to.