"Ladies, ladies," Peter said, "Let's all calm down. Black Cat, this is Spoiler, who is dating Robin and anything we do have would be strictly platonic and would remain as such. I hope that we could be friends, but there is nothing, absolutely, never will be. I do'nt know why I'm explaining this to you..." Because yes, Black Cat was attractive, and flirted with him and...
Gwen. It always came back to her. With Gwen he connected intellectually and could share all these dumb romantic things and she'd find them sweet. With Black Cat, they shared the city at night but he didn't want the world of Spider-man to mix with that of Peter Parker. The two had to stay separate.
"So there's a light here and apparently I'm breaking some sort of copyright," he sighed, "I need a lawyer. And a PR guy."