How do I help my boyfriend gain weight?

It hurts me how toned he is but skinny. During sex when he’s on top he’ll hurt me with his waist sometimes & it’s sad to be honest. His wrist is small too. I used to be skinny so I bought protein & makes sure he eats 3 meals and snacks & he’s been good but some days he’ll sleep late & wake up late. Im scared i’m going to give up on him eventually with the weight journey because it’s been months.
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By the way i wouldn't give up on him just his weight gain journey ^
How do I help my boyfriend gain weight?
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