Is this a valid reason to be pissed or is just my hormones?!

Ok... I'm seriously on the verge of leaving a 10yr marriage, we just had another baby 7 weeks ago and I know my hormones are all over the place but I think I have a reason to be upset! My step son who was supposed to move out on his own moved in with us because he got fired from his job for stealing over 3,000 on company credit cards (He worked for his grandfathers company) and he basically had a falling out over at his Moms. So since he was broke he moved to our house the deal was he had to get a job and go to school or join the military, just do something! Anyway he's been here for 2 weeks and has NO job and literally wakes up to smoke pot and hang with his friends. I told my husband I did not want him driving my brand new car and he let him do it anyway and he totaled it last Thursday because he wanted to cut someone off but wasn't paying attention! I'm furious and when I lost my sh*t about the car my husband freaked out on me! He always makes excuses for him unless he's mad or his feelings get hurt and he chews him out but 2 seconds later it's back to the same crap. He bought him a new cell phone behind my back spent over $300 and tried to lie about it... And to top everything off tonight they went and looked at a Jeep and they bought it so they can fix it up together!! My car that I only had for 22 days is totaled and they go get a Jeep... I guess I'll take care of our newborn by myself? I've tried talking to him, yelling, having a date night everything to try to get him to compermise and we all work together but it's pointless it feels like. Everything has changed in our relationship and I resent him for putting my through all this stress my milk started drying up which I've taken really hard I tried have sex with him it lasted 2.2 seconds so I start thinking I'm unattractive now.. Uhhh this is just not how I envisioned our first months with a newborn.