I have this line in gaydate that I'd like to adjust and expand on a bit for a psl.
Basically two brothers meet on a dating site but don't know it's each other. After talking for a while, they decide to meet up at a hotel room and surprise! they find out they've been talking to each other the whole time. They decide to go forward with the hook up anyway and something romantic starts between the two. They go out on public dates and act like a couple, not caring who sees them.
It could extend to marriage and children if the line go on long enough but that's the base for it.