The only part I remember from the manga is when the top/seme goes to undress the bottom/uke and he notices him wearing panties. The seme asks him about the panties and that's when the uke explains his girlfriend makes him wear it to make sure he doesn't fool around with other people.

I know I've read this before but cant seem to find it anywhere....atleast in my history and poorly managed lists. A bit of details....do you remember it being the main story or just a random side story?
My mind's been in a chaos because of this.

I can't remember if it was a main or side story but I do remember the bottom/uke having glasses and short hair. If I'm remembering his appearance correctly. I hope that helps a little. Sorry this reply is late!

I'm pretty sure it's Ai ga Matteru by Abe Akane.

.....and it is. Thanks a bunch mate.