Am I overreacting? If I leave him it’s gonna be cause of his mom!

Ok so we’ve been having a lot of issues due to his mom, who lost her job on purpose! She can’t fool me... anyways she’s been sick ( except when it’s about partying ) to look for a new job, excuse after excuse... We had to move in to her place due to another problem she caused us with our ex Roomate, and this month of course my bf had to pay for all the bills, rent electric bill groceries etc, and she was demanding money to fix her car with my bf said he couldn’t cause we were already low on funds and this month on the 17 (could be before or after) is my due date.

So a few days ago I asked him not to let her use our car cause we might need it to rush to the hospital plus she has no money to put gas in there and we live pretty far away from everything so a trip to the closest store takes a lot of gas... he agreed and said that that was a good idea bla bla bla... And what happened today? She slept all day arguing she was feeling terribly sick again, so we decided to clean the whole place when like 20 minutes ago she comes out of her room asking for our car keys cause she was going out... so I was thought that my bf would say no... and he said that if she was going to drink maybe it wasn’t a good idea and she said that she wouldn’t , then he said I wanna go to but i can’t cause I have to stay with her, so I thought he would point out that I’m really close to

My due date... but no, he let her take the car WTF? I rarely ask for anything so I’m

Really pissed right now! Am I overreacting? Is it wrong that I worry about this stuff ? I don’t care that she is a party animal I just don’t like her using our resources which aren’t much to do it ! We’re always struggling cause of her... if I leave him it’s gonna be due to his mom...