Recently, your ex wanted to get back with you but since you were with Alejandro you refused. Even tho you didn't want to get back with your ex, for some reason he got really mad when he found out about it. He was scared that you might change your mind and leave him for your ex, that's why you two were having an argument right now.

"Name one way I'm better than that guy." Alejandro said, clearly wanting some reassurance from you.