Advice????

K so my fiancé got a brand new mustang a couple months before we met and now we have a baby on the way and need a bigger car and he keeps saying that we should just get a second car instead of trading it in but it will be two insurances, twice the gas, and we'll still have to pay his $500 monthly payment for the mustang. I know 100% that if we WERE to get a second car, he would just drive that car to work rather than the mustang because the mustang is horrible on gas and his work is 30 minutes away. It keeps starting fights and I don't know how to get him to understand that we can't afford two cars. We live in an apartment so it's not like we have a garage to store the mustang either.