I'm thinner and more muscular than my ex
Why are you comparing your body to your ex's body?
I'm glad I looked better than her
It's not nice to be judging other people based on their body type.  Men and women tend to look different naturally, and however your ex looks is just something about her that she can't change easily.
I'm not judging, I'm just saying that I'm more attractive than her.
Bringing up your body type and how you looks is not nice when talking about your ex. Chances are, you and your ex did not break up solely because of how you look. Saying that you are more attractive then her kind of seems like kicking someone when they are down.