Just Another Casual Encounter?

Well, today was just another day until I got a message from an old student named Alex. We're both in our 30s now, and we started chatting like old friends. The flirting was subtle but present. When he invited me over for coffee at his place after class, I didn't think too much of it. But then came the texts about how much hotter I look as a teacher compared to high school, and how he couldn’t wait until after hours when we could talk more. I ended up staying for what was supposed to be casual coffee but turned into something else entirely. The irony is, with my open relationship, it should have been no big deal, but the guilt? It’s like bringing a new flavor of ice cream home and hoping your partner won’t notice that it tastes different from usual.