Hi Sofi,
He must be a Special Kitty for you to try
so hard to help him this way.That's great.
If you spend time in the room with him, even
if it's just reading a book or watching TV,
and just let him "experience your presence"
it will help him pick up your scent, and
gradually learn he has nothing to fear.
It does take time & patience and a real
commitment to helping him learn to trust you.
It can be done. Don't force him to come out
of hiding, he will do that when he's ready.
Spend some time in the room with him, and
maybe leave something behind when you go
like a sock or shirt,etc. It helps if you
go ahead and talk to him ,in soft reassuring tones. Doesn't matter what you talk about,
just let him hear your voice talking in
a calm relaxed tone of voice.
Best of luck to you. Sounds like you really
want a better life for this little guy...