That look a girl gives you when she's fighting her urges.

"Everything okay Tabs?" you ask her, knowing things certainly aren't okay but out of politeness having to ask. Her almost pained expression as she tells you it's her heat, that you should leave if you don't want to mate suggests that she's losing a fight in her mind, that she's succumbing to the hormones raging through her body, the biological urge to mate with a male, to procreate and make cubs. With your erection raging, and a chance to breed the girl you've desired for so long, there's no way you'll turn down mating with her, giving her a cub.

You know in the throes of heat she can't think straight, that the only way this ends without breeding her is if you walk away, but you can't, you just can't. You stand like you plan to leave, but instead step closer to her, kneel beside her, kiss her, whisper in her ear. "I'm staying Tabs. I know what it means, I know what will happen, and I hope you invited me over knowing full well this would most likely happen."

Your decision made, you step back and begin to undress, there was no need to keep them on, not when you know what's coming, literally and figuratively. It doesn't take Summer long to take off her dress, the beautiful young feline standing before you in the prime of her life, fertile, and in heat. Everything a young male in the prime of his life, equally fit and fertile, could ask for.