Yaoi I recommend (There are also few Shounen Ai manga)

Age difference, the younger boy is very cute ><

BDSM

Teacher and student

Harassment, rape, might be very uncomfortable for someone

Threesome

Has time travel

His first love turned out to be a male

This was my very first yaoi content I've ever read and I recommend it very much

Teacher-student relationship

I still can't process it how can such a big dick fit into the small human's ass...