any veterinarians in the house?!

sw

Me and my SO got into a heated discussion tonight about my rescue cat I had gotten from a shelter. we found a flea in the house. and I give her the monthly flea meds and everything, I've never seen a flea on her. But there it was, right on his leg. He's slightly tipsy (a few beers after work), and told me she has to go outside if she has fleas. umm. Not happening! he'll be sleeping outside with her if thats the case. anyways, I was wondering if there's any veternaians on here that would have some advice for flea control. or any other with experience with this. I've been using biospot, and I'm not even sure how she could get fleas to start with since she's solely an inside kitty. I've only had her a couple months, she goes to the vet to get fixed in two weeks and I could ask them then, but is there something I've done wrong in preventing fleas?? is biospot crap?? any good alternatives out there? any input is appreciated