How exactly might this genetic experiment occur? I know this is meant to be fantasy, but it never hurts to have a grain of reality in there somewhere IMO. And what would this guy's biology be? As far as physique goes, he looks about the same as a normal human except with pointy cat ears, a tail, claw-like nails (I don't think they could retract like a real cat's) and possibly some fangs. Also, he has hunting instincts/abilities comparable to say, a lion or cheetah (given his sleek body he may be more like the latter), and since his rescuer and his girlfriend want him to somehow become a normal member of society, this presents quite a challenge. But other than all that, I don't know.
I haven't done any Google-ing as I don't really know WHAT to Google, so in addition to regular suggestions, suggestions for search terms are warmly welcomed.