I believe there was a forum for shippings and that kind of stuff, but I don't think it's completely offtopic here lol.
It was kinda confirmed that Ryoma and Sakuno had a thing (or at least they will have in the future), one of the drawings of the PoT characters in the future kinda show it.
How about any 3rd party?lol
I would say his cat Karupin...as he carries a picture of that in his locker...
...Sai is right.
RYOMA IS ZOOPHILIC
Nah, seriously, it's either something yaoi or Sakuno... your pick
Ryoma loves tennis, indeed he will marry a tennis ball and have children with it lol.