Hey, good taste in cars (I have a 2005 GT).
I agree with what previous posters said...unless your ex-boyfriend had a Mustang (in which case I could see his point) he's being incredibly immature, controlling, and manipulative.
I dated a guy once who wanted all my attention too, and trust me, its no way to go. He got mad at me once for spending
25 minutes updating my planner while he was over at my house. I said, "would you mind if I just sat and finished this?" and he sat on my couch and chilled out. 25 minutes later I finished, & he was up in arms that it was "stupid and pointless" for him to even be there if I wasn't going to "pay any attention" to him.
Don't make the mistake of staying with someone like that.