Fiancé is getting fat

Ni

How do I tell my SO he is getting fat? He has gotten soooo greedy over the past few months and gained about 20 pounds, even his mother noticed when we went to visit her. I like my men big don’t get me wrong but not like greasy big, always eating big. What should I do? I’m thinking about putting him on a diet or dieting with him?? But then again if I am pregnant I can’t diet because pregnancy just don’t let you do that. However I must say he has picked up my eating habits, I love sweets and carbs and stuff and when I met him he wasn’t like that at all. He pretty much let’s me do what I want so doing a whole meal plan diet thing shouldn’t be much? Would it be offensive? Btw I am 130 pounds if that matters, he’s about 260.