Why the guy I'm seeing starting to lose weight a lot but me getting fat?

most people told me that I'm not fat, but I feel like I'm chubby, some fat on the stomach, my bare butt look out of proportioned, my waist getting wider, my thighs looks big, my face became puffy.. when I checked my BMI, it's still healthy..

Why the guy I'm seeing starting to lose weight a lot but me getting fat?
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