Dilemma, what should I do?

[CombatEX]

"I have lost this game. I can see it, and I'm pretty sure my opponent can see it." In that case I would forfeit.

If you're really that sure your opponent would have beaten you if not for their misclick then just give them the win. If you're playing at a low level though where your opponent could easily overlook the fact that they could beat you on the next turn, it's not as clear what course of action you should take.

But anyway, if your opponent is at least masters just forfeit.