He started going to the gym after making me his girlfriend?

I'll be honest, I'm a "thicker" woman. I don't go to the gym at all or workout. I'm 5'3" and 167lbs but not overly gross looking, it kinda evens out on me but bmi wise I am overweight. My stomach is a little but "chubby" but nothing crazy. This great guy made me his girlfriend a month ago. When we first met he told me he also never goes to the gym. We have had s*x and now he's starting to go to the gym... I mean good for him but I'm a little worried on if he's trying to get more muscle to find someone better? He already was in my opinion, average weight and smaller than me chubby wise. So I'm feeling a little insecure about this, any thoughts?
He started going to the gym after making me his girlfriend?
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