hello, I'm sorry for your loss, how young is your baby, and does he eat solid food by himself?
Since your baby has diarea, make sure he stays hydrated (you can do the tent test to see if he is dehydrated by pinching gently and pulling the skin between his shoulders, if the skin doesnt go back in pace immediately, then he is dehydrated and needs fluids, in which case you can give him pedialyte or gatorade).
Since he is now alone, make sure to spend much time with him and has plenty of toys to keep him occupied (the ideal would be to find him another mate ultimately though)
Fruits and vegetables are good, but not enough, he needs proteins as well.
On the long run, you will need to chose a balanced diet plan (there are several well-established and widely used diets) for your baby. Depending on what you can find locally, BML can be a solution. I personally use SGS2, which is quite simple and on which my gliders do well, but it has the downside that it requires to imports Wombaroo HPS (I get it from the UK).
For a short amount of time, you can give him fruits, vegetables (but
NO onions, garlic, leeks or anything of that kind which are toxic to gliders) alongside yoghurt and either hard boiled eggs or boiled chicken / turkey.
Here are links to some widely used diets:
BML
TPG/Pricilla Price diet
(
requires TPG multivitamins)
OHPW
(
requires Wombaroo High Protein Supplement)
SGS2
(
requires Wombaroo High Protein Supplement)
There are other diets, those are just the ones I have personally used through the years