which one is recommened?

to eat two or three meals a day?
i dont take lunch to school and i have breakfast but sometimes dont have dinner because i feel tired and go to sleep

Three is standard – it is healthy to be eating throughout the day. If for whatever reason you cannot manage three, make sure you have two large meals as well as some decent snacks. Not eating enough, or frequently enough, will just make you more tired! And you'll be grumpier, find it harder to concentrate… and there are many serious consequences to your health that can result from not eating enough.
Is there any particular reason why you don't take lunch to school?

yes i use to bring lunch to school and i wanted to sit with a group of ppl in my year, but one person in the group didn't like this and decided to betray me
after a few months i was sitting by myself because i felt it was all my fault, and felt ppl staring at me which cause me to want to hide away and not bring lunch again

Does it really matter if you're sitting by yourself? If there's no one you want to sit with, then sit by yourself. It's totally ok to do that. Could you maybe bring a book to read whilst you have lunch? And if there are any people you think you might like to sit with, ask if they'd mind if you sat with them/at the same table.
People probably are not staring at you, they probably don't even care what others are doing – they'll be more interested in enjoying their lunch.

i feel that being alone is better because i dont have to worry abt a conversation
and yes i could bring a book
but i also dont want the same thing to happen again
also i see ppl with their friends and just want to hide away