JKR stated in an interview (transcribed on her old site) that Tom Riddle has categorically never loved, nor cared for anyone at all.

Q. Has Voldemort or Tom Riddle ever cared for or loved anyone?

JKR: Now, that’s a cracking question to end with—very good. No, never. If he had, he couldn’t possibly be what he is.

As to why he's loveless, this is largely down to the fact that his mummy didn't love him.

Ravleen: How much does the fact that Voldemort was conceived under a love potion have to do with his nonability to understand love is it more symbolic?

J.K. Rowling: It was a symbolic way of showing that he came from a loveless union - but of course, everything would have changed if Merope had survived and raised him herself and loved him.