Health advice

This may seem odd but please bare with me.

I need some advice on how to gain weight and not for me but my fiance. We have recently started tackling his mental health; as it is something we wanted semi-regulated before our wedding. But with that came the discovery of other illnesses. Since we started this journey, just shy of a year ago, my 5' 11" fiance dropped from 185lbs to 124lbs.

Thankfully, we think he is on the correct type of medication and can focus on getting him back to the proper weight. He is a very private person and didn't want friend of family knowing what is going on so this was the only place I could think of to ask for any help.

He is a very picky eater and has some paranoia related to food so he can't just eat. We are going to start by trying the instant breakfasts and muscle milk.

If there is anything that has worked that you know of please share it. We are up for trying anything.