I'll play the devil's advocate...
You should get the Mustang. But only if he'll grow a mullet and wear sleeveless flannel shirts. That way people can see who's idea it was to get a Ford "stang".
Ok 4 real, it's ur car not his, he has no right to tell you what to do. Your life as well, follow your heart and love and make sure you don't step into a relationship where he calls the shots. It's should be a two way street. Let him get the Stanger, but make is a 67 1/2 not a 2005, yucko, but that is just IMO. Drive what ever you want.
Mod up the car you love, they stopped making them and disappearing fast, get better gas mileage and a hot girl in a hot car just don't get any better IMO.
Good luck either way