C4C, as always.

You used to screw loose girls
at parties when you were away for that year;
I never complained.

The girl at the ice cream shop
was checking me out today,
but I couldn't tell
if it was because I'd gone to school with her
or because she wanted me -
I thought it was probably both.

I wanted to sleep with her,
but I thought of you
and knew you wouldn't approve.

I hope you won't complain.
Does it really matter
so long as I brushed my teeth afterwards?
The illegality of cannabis is outrageous, an impediment to full utilization of a drug which helps produce the serenity and insight, sensitivity and fellowship so desperately needed in this increasingly mad and dangerous world.
- Carl Sagan
Clever. The line break and comma at "was checking me out today" creates a pun that you don't over-do after. The automatic response of "she's looking at me because she wants me" tempered by the (more realistic) thought that the girl just recognizes you works well. And the personal guilt at the mundane act of wanting a girl while buying ice cream despite the other party's wanton and (ostensibly) drunken act of scissoring/going down on another girl provides a simple, real contrast between the speaker and subject.

What could be strengthened is the link between the two actions. Good choice on the indulgence of ice cream, as it conveys sympathy for the girl (?) in question in the carnal sense. The problem is that there's no balance. "You did some girls when we were away. I thought about doing a girl when I bought ice cream. At least I brushed my teeth. Whatevs." The big issue is the dismissive nature of the piece.

All in all, not bad. I wouldn't change much, but I'd add some.

My birthday's in just under 4 hours in my time zone. Crit my piece, please. Attention is a great present. https://www.ultimate-guitar.com/forum/showthread.php?t=1456459
I am a fake mountain.