The moment he pulled back I would have grabbed anything close to hand and walloped him on his backside hard.
I would then have untied him given him a good chase around in a small circle until he thought I was the devil himself.
He would have forgotten all about Selena because he would be worried about blinking without my permission.
As for riding him then wet or not - and neither you nor him are made of sugar so you will not melt - I would have worked him into the ground. Forget about softening at the poll, forget about getting him to work sensibly, work him hard at a trot and canter until he is ready to listen.
It is no good thinking that he will focus as he gets older - even if he were a yearling I would insist that he focuses on me when I am doing anything to him.