My cat has stopped using the litter box since we got a second cat. What do I do?

I have a beautiful 2yr old black and white male cat who has always faithfully used the litter box. 6 months ago we got a second kitten and while he loves playing with her, he now refuses to go in any box she's been in. And she's always going in them. We have 3 boxes in different areas in hopes that he can have his own, but the new cat uses all three. My parents are threatening to get rid of him, because he's been consistently going on our couch, beds, and other furniture, sometimes even next to the litter box. I'd appreciate any suggestions to change his behavior.