Basically what's going on is my mom and I have some issues. I'm fifteen but I don't act my age at all, I'm incredibly responsible and have the mindset of someone much older than me. In fact I'm so different from all the other kids my age that I don't have any friends. My mom is pretty much the exact opposite of me. She's irresponsible and has never had her together. I remember her taking me to her friend’s house so they could smoke pot from the time I was three which always pissed me off because it was so wildly inappropriate. My dad died when I was 6 months old and I've gone back and forth in blaming her for his death. I say that if I had been better and more loveable he wouldn't have felt the need to do drugs and if she had been more supportive and she saw him slipping up after rehab she shouldn't have gone out of state for a wedding. She has always relied on someone else. She doesn't work so my grandparents have to buy me everything which I feel incredibly guilty about and we live with my step dad who is emotionally abusive. She cheated on him two summers ago so now I have an 11 month old brother. Although she takes fairly good care of him she couldn’t even get her act together when she was pregnant and she smoked the entire time and that infuriated me beyond belief. My step dad for some reason loves my brother even though it's not his baby. This is really all background for my question. It seems like things with my mom are either pretty good or pretty bad. And to complicate things even further my step dad will treat me like a piece of garbage and then turn around and play with my brother and my mom won't say anything or stand up for me. I feel like she’s a child in the body of a 42 year old. She is a perpetual teenager. When she’s in a bad mood she blames me that I don’t help more with my brother but I help out when it’s reasonable and I tell her I’m not the one who hooked up and got pregnant so why should I be the one to suffer the consequences and care for the baby? While I totally adore my brother and am madly in love with him, I feel like she should give me some freedom because even though I don’t act like it, I am a teenager. And she has completely ed me over with college. I want to become an architect and that’s a good 6-7 years of schooling and the certification process is slow, expensive, and extremely difficult. I’ve seen what happens when a woman is dependent on her husband or boyfriend and I don’t want to be that person. My mom dropped out of high school and never got an education even though my grandparents were willing to pay for EVERYTHING. I’m not kidding they put my aunt through NYU, how could she turn down an offer like that? Anyway in her typical style she never saved any money for college she just assumed that because my dad died I’ll get some sort of benefits. This is another big issue between us. The biggest problem between us is her lack of responsibility and ambition. Everything is my fault with her. The house is dirty? My fault. We’re out of food? My fault? She’s low on gas? My fault. She has her good days which is about 60% of the time and she’s pretty good then. And it’s not like I hate her and I think that’s the worst part out of all of this. Even though I’ve been through hell and most of it could have been prevented by her I still love her so incredibly much so it kills me when she gets mad and ignores me for days on end. And it’s incredibly hurtful to see her stand there while my step dad takes all his frustrations and problems out on me in the form of verbal attacks. I know damn well she could step in and say something but she doesn’t. Wow this has gotten really long I think I need to wrap this up. SO why does she act like this? Is there something I could do better or do I need to just figure out that she’s an extremely flawed person and come to terms with the fact that I’ll never have a normal life unless I move out and provide one for myself.

Welcome to the Club. Of all families, in all their variety of disfunction. No fun when I was your age either, and I didn't even have a stepparent.
What do you do? You bide your time. You aren't going to change your mother, or your step father, and you can analyse your mother until the cows come home.
Your question is why does your mother act the way she does, and we can't possibly answer that. You know her better than we do, which is not at all, and you seem to have a pretty good sense of things for a 15 year old. It's common for any child to wonder how much is his or her fault. My mother was never happy a day in her life and I tried constantly to be the best daughter I could be - best in school, best in everything, and of course none of it 'worked' because I wasn't really the cause of her misery. So what can you do? Try to be good around the house, try to be appreciative of the roof over your head and food on the table, and keep your sense of who you are. I lost mine as a teen. I lost all sense of what I wanted out of life, went to a top college based on all my As and high SATs, and then dropped out almost immediately, since none of the ambition came from within. So keep your dream alive about who you are and who you want to be. Who knows what your mother went through growing up? Who knows why she had an affair? For all you know, your step father had one first (just sayin', you can't judge).
Go talk to your grandparents and if they are far away, plan a visit this summer. Tell them you feel bad about them supporting you and tell them about your plans for college and what your interests are. Get to know them well. I'll bet they will love it. It's a gift you can give them for all they do financially.

Oh and drop that guilt from when you were 6 months old. How can your dad's death possibly be your fault? (I have a feeling you know that but feel guilty anyway. I know THAT feeling.) It isn't even your mother's fault. Most addicts out of rehab fail and fail and fail again. Your mother can be the most irresponsible person in the world but it still isn't her fault that he was an addict who failed again and died. Telling yourself all this is one thing. Actuating it is another. It takes work, and time.

Everyone has problems with families. Some more, some less. Unless there is some changes we can make, we have to live with it until we can move out. It takes time to get over things, and some things we always remember, but it does get easier.

I think you need to talk to someone about your extreme anger - which shows loud and clear - at your mother. I see you reading her mind at every twist and turn, and I see no compassion at all in you. Maybe she's doing the best she can. Maybe not. I'm sure your attitude on the board when you write this shows loud and clear when you interact with her.

Blaming her even in part for your father's death is unfair unless, of course, she stuck the needle in his arm.

Yes, all families have problems but I think your undercurrent of anger, judging everyone for everything, is over the top. I see a list of everyone's faults but your own - you have none?