Okay. There are healthier options at restaurants if you do
go out. (Or I should say when, because chances are it'll be really tough to never
go out.) It takes some planning, but you can often find the healthier choices online if you decide on the restaurant ahead of time.
You don't only need to plan one day to cook at home. Of course you guys can cook! In fact, why don't you change that dynamic and start cooking for them. Doesn't have to be complicated, and it doesn't have to just be salads. There are simple recipes all over 3FC, take some time, find a couple you might want to try, and go for it
About your birthday, is it special enough to you that you want to have a piece of cake and a drink or two? (I ask, because my birthday is not special to me.) If it is, then PLAN to have A PIECE of cake and maybe a drink or two. PLAN! That's all it takes