this has happened before and apparently it could be a side effect of the white spot medicine he's been taking (think it's finally gone hooray!!)

do you think it hurts him?

he seems happy enough i just wondered that's all

So long as it's just a tear and not fin rot he should be ok and it should heal in a couple of weeks, just keep an eye on him to make sure it doesn't get any worse, it happened to mine but they're ok now and they had been treated for ick.

We have a fantail bully, his name is Willy and we've had him for years. The problem is that we have had the other two goldfish, one bigger than Willy, called Billy and the smallest is Moby. Willy keeps nudging their backsides all the time, which leads me to think that Willy is the male and the big and small, Billy and Moby are female. Is Willy making their lives a misery?

It's so hard to tell which sex they are, I'd keep a close eye on them for signs of stress, you may need to seperate them.
This was a problem with two of mine even tho they were from the same tank in the shop, Mack the small one did the nudging to Mabel the bigger one even tho they seemed to get on most of the time, poor Mabel died .