Dear Top,
The reason why school-external and inter-year romances are so heavily discouraged, is exactly to prevent you from finding an outlet for your sexual frustrations that isn't competing with you and doesn't require complicated plotting. Your problem seems unsolvable specifically because I ordered rules set in place to prevent it from being solved.
If you find a clever solution, write me back about it and I'll give you a prize before I put in place new rules to prevent it from happening again.