is it rude to comment on your s/o weight

My fiancé has lost a lot of weight he weighs 130 thats the same as me  i practically where his clothes, i love him no matter what but he's starting to look sick some he could pass for a 16 year old and his mom had the nerve to ask if i feed him i do ! He goes all dat without eating until he comes home for dinner, its hard for me to get on top during sex because i feel like im squishing him!