mom issues😒😒

I know this part is going to sound like typical mother daughter arguments, but anytime my mom and I have a disagreement it just unlocks all this anger I have towards her. About 2 years ago I found out my mom was having an affair with my stepdads best friend and she would talk to me about it like we were friends in high school and it put me in such a bad place because I love my step dad, he raised me, he was there for me since I was born bc my real dad was an asshole and ditched my mom and I.  So when she told me I was heartbroken and I tried telling her like it wasn't ok she shouldn't be telling me this or doing it and she just played it off like it's normal. The secrets and sneaking around just ate up my emotions and I tried to kill myself which lead to me going to rehab for depression. During that period, my therapist would have her talk to me in sessions and let out feelings, and my therapist would say she's only human people make mistakes and I get that but one time is a mistake, having an entire relationship with another married man who's your husbands best friend, not to mention I have 5 siblings, like that's not some small mistake. I know my mom has been through hell with past marriages but why be unfaithful to a man you have kids with and takes care of you. I worked really hard on trying to communicate better with my mom but then a few months after I left the hospital, I found out she was having another affair with her boss. She had the nerve to bring my siblings and I to his house too. She would give his grown ass daughter, who has a baby, rides and money (she'd spend on drugs)  but she was always late picking up my siblings and she doesn't even go grocery shopping like wth, she's trying to take care of someone else's family but she neglects her own. I dated this guy for a long time, he cheated on me and I told my mom and she said "well that's life" no kind of simpathy or emotion. She acts so entitled, she steals from my older sister, she took my sisters cash for rent out of her car and when my sister confronted her she said "I'm your mom you owe me" she steals from my little sister too who's 12 and saves up for clothes or food bc my mom only goes shopping for my siblings once a month unless she's buying make up or her own stuff. Whenever I'm upset, she tries to just buy stuff for me to make me happy, but that's not how happiness works and she only buys stuff that she likes bc she knows I won't accept it/use it. She doesn't take any responsibility for anything, and she wasn't always like this, that's what bothers me. When my stepdad bought her this house and she had my 5th sibling everything was okay, she was happy and actually concerned for us now she's greedy and careless. I love my mom and I know nobody's perfect but she doesn't even try to be there for me or any of my siblings anymore. I'm 18 and my siblings are still kids: 12,9,7, and 6. My mom is a good person to everyone else, she gives her friends rides, helps them with money but when me or my siblings ask to go somewhere or have money for lunch it's too much. Sorry this is long, I have no one to talk about this with, my boyfriend is close to his mom so he's always like well she's ur mom you have to love her, she bought you a car (she didn't, it was child support money and it's in my step dads name, and he pays for it) but yea my bf thinks my mom does anything nice even if it's small, it makes up for all the hurt she put me through. What really gets me though, is when I was in the hospital after I tried to off myself, she said "I'm glad you didn't die bc I can't afford a funeral right now, we have bills and now a hospital bill" and she never apologized, that's not funny either. I help out with my siblings and around the house a lot and she can't even genuinely apologize for putting me through that. I love my mom but she hurts me so much emotionally.