Is it normal to think that his mom should be grateful to me???

My son's friend practically lives here and has done so for the past 7 years. His Mom is a single Mother who has a revolving door of men in her shitty little apartment, she drinks, she goes clubbing, she rarely ever buys her son food or clothing and quite frankly, I don't think that she deserves to call herself this boy's Mom. I tried confronting her about it but all she does is give me some speech about how I don't understand how hard it is to be a single Mom. Whatever.

I care for her son and he is part of our family. Whenever he needs clothing, a doctor's visit or anything of the like, he comes to me. Most of his stuff is here too and he sleeps in the top bunk of our son's bunk bed. For all intents and purposes, he is my son and I love him dearly. Our lives are peaceful and she is too occupied with her own bullshit to care about her son or what he does. He sleeps over there occasionally but usually he is here.

Sometimes she can't help herself, though. At least once every 2 or 3 months she comes knocking at our door wondering where her son is and being a complete bitch about it. She complains about the clothes we let him wear or the bed in which he sleeps and that he has to share a room with our son or that our house is messy (which it is only barely) or that we feed him too much fast food (we have Pizza on wednesdays like clock-work, otherwise, we cook) and she complains that I am taking her son and just says nasty shit about how she is going to call the cops on us if we don't quit letting him stay over here. Of course, she becomes sober again and goes home, but really? I am raising YOUR kid and you come over complaining about how I am not doing a good enough job of raising YOUR son?

I really think that she should just shut her mouth (or stuff another cock in it) and leave us at peace. I can't wait until that kid is 18 and we don't have to hear her hell anymore. I think she should just be grateful that someone cares about her son.