Second guessing

My SO got a job Friday and they told him he needs his own transportation to get to and from all the buildings he's doing maintenance for. He tried to get financing on his own but wasn't approved. He asked me to apply and I did. I was approved and we are supposed to go get him a vehicle today. I'm second guessing helping because things have been kinda rocky. We argue and it always turns into him asking if I want him to leave. Even little things he gets so mad. Last night I found something that looked like a vibrator in our couch his mom gave us. I knew it wasn't a vibrator though and asked him to show it to his mom. He sends her a text like WTF mom and convinced her it's a vibrator and she needs to talk to his 16 year old baby sister. I looked up the serial # and it's a fucking smart pen/usb...I showed him and he was like OMG you just always have to be right...Umm no kinda just saved his sis from an awkward conversation about vibrators. Then this morning he shows me a meme that kinda pokes fun at my insecurities and a funny video about people who don't understand simple things and goes, this reminds me of you...WTF...way to show your confidence in my capabilities...I make twice as much as he will at this new job and have established a career and respect amongst my peers. Why when he needs me to get something he needs to keep his job is he making me feel this way?!? I'd be super nice to someone who is about to be the only reason I can keep the first job I got making double digits an hour...IDK I want him to help support this baby but I don't know that I want to with him being so disrespectful just because...