My indoor-only kitty is also a needy little love sponge. He really hates other cats though. I've fostered lots of other cats over the years of varying types -- young, old, male, female -- and always followed the advice to slowly introduce them, etc. Never worked, he hated them all! He just wants affection from people.
BTW, I had the same problem of feeling guilty that I left him alone all day. I ended up getting a window bird feeder to keep him entertained and he loves the damn thing. Sits there watching it with his tail twitching all day. And sometimes he tries to pounce! The window is full of paw prints and nose prints... he will never figure out he can't eat the birds through the window
