My 10 yr old female cat keeps hissing and biting my boyfriend. Help?

Hi - I have a 10 year old female cat that is the sweetest thing ever. I have recently moved in with my boyfriend of 3 years and the longer we are living together the more skid-dish she is becoming of my boyfriend. He would play with here to the point where she would give a hiss and small nibbles, but now she won't even let him touch her with out her fur standing up on edge and she gets into the fighting position with a warning hiss! She's always been great with people but i think the "playing" has now got her to the point where she's always on the defense. How do we try to fix this?? My boyfriend really loves her and he gets his feelings hurt that now he can't even touch her... what do we