Doesn't this make him selfish? What should I do about my car keep or return?

I bought a used car 2014 mustang at dealer had some scratches on it but that was the lowest mileage I could find. I took it to an auto shop and they showed me rust underneath the car and wheels where the brakes are which is causing it to squeal when it is used. The worker at shop (not dealer) told me its not too much rust so nothing to worry about.
Later on I found rust under both seats. Which got me so worried because I dont want to spend more money to fix it up. I can still return it and get full refund. My boyfriend was telling me to look for another mustang. So first search I did I found same year and even less mileage for less price. I said "oh I found one!" Then he got my phone and messaged him and we seen the car looks great condition. Now he's saying he wants to buy it for himself. Like wtf? Isn't that selfish? I need to replace my car and now all of a sudden he wants to buy the car that I found and wanted to buy. I feel irritated because im stressing out not sure what to fuckin do. Should I return the rust car or keep rust car if he buys that mustang for himself? My car came from rhode Island not sure if its moisture or flood. Carfax said no damage reported. I'm worried mine is a salvage car
Rust under seats
Rust under seats
Rust under passenger/driver seat
Rust under passenger/driver seat
Updates
+1 y
He keeps asking if I would get mad if he buys it for himself. I just say "no do what you want." Because im not selfish like him. But deep inside im mad at him.. really disappointed too shows how much he cares
Updates
+1 y
This morning I asked both my siblings to borrow 5k and they lend it to me. I told my boyfriend I have the money and can buy it and it was ridiculous he made a huge big deal and argument of how much he wants it and if I buy it im kicked out. I told him fine go have the car im not the type of person who is going to ruin a relationship like him. I feel like shit cuz he bought the car and now he's shoving it in my face. I think its pretty fucked up.
Doesn't this make him selfish? What should I do about my car keep or return?
Post Opinion