This is just my personal opinion. I think he feels lonely, but at the same time satisfied.
His love has been, is, and always will be unilateral. It is not that he has never been loved; however, he always denies such love access to him. As long as he loves others, he feels connected to them and satisfied.
When he wants to use you, he does allow you to get close to him. But there will still be a thick wall between you and his heart.
Sounds pretentious, doesn't it? But those were his very own smug words in my chatroom that day. Talk to him if you want to complain. Though I don't think he even blushed when he said those words. Well.
This unblushing attitude, I think, is exactly what keeps him in the advantageous position, whatever the situation. Even so, he still keeps saying things like "Because I love all the humans in this world, all the humans in this world should love me back." Well, whether it's a lie or not, it does sound like something he would say.
But if you were to ask me, "Does Orihara Izaya love himself, then?" - I would have no answer for you but silence.
That's something only Izaya himself knows. Whatever he chooses to tell you, there is nothing you can do about it.
Because even if people try to persuade him to change himself, he would probably never let their words sink into his heart.
That was my opinion.
Sorry. To be frank with you, I feel embarrassed."
-Tsukumoya Shinichi