So I just got that final scene and I feel kind of upset and tricked. Out of nowhere they started talking about a "watch word" and it seems like Bull has been having rough and painful sex with my inquisitor. I was pretty weirded out by this but there were no dialogue options other than to go along with it. I wonder if there was a dialogue glitch because we had never talked about this before.
No no no no no no no. It wasn't rough and painful. It might have been rough, but only as rough as your Inquisitor would allow it (that is up to your head canon of the scene). Bull makes it VERY clear that he will not hurt you without your permission, or make you fear him (unless that is what you're into). He won't do anything without your consent. That, and he gave you 3 chances to back away and call it off in the very first scene.
The watchword is for obvious safety reasons; even for a Qunari Bull is a big guy. I don't know what race you play as, if you play a Qunari it wouldn't be that obvious I think, but if you pair him up with a human, an elf or a dwarf... yeah. That's why insists you have a watchword. He doesn't want to hurt you and I'm 100% convinced he'll do whatever he can to minimize it as much as possible, but with that size difference there is gonna be some.
I think Cole mentioned something like this in a party banter; that yes, Bull is a dominant top... but if you think about it, the inquisitor is still in charge, because he/she decides how rough (or what have you) it will go, and when it stops.
Just because Bull's body language when he comes on to you implies that this is gonna have a D/S theme, doesn't mean it's gonna be chains and gags and blindfolds and painful sex. I fully believe Bull can be very gentle (he has to be, he can easily break people in half if he's not careful, especially with someone smaller like an elf).
The fact that the Inquisitor's comfort seems to be top priority for him definitely makes him one of the best romance options in the game in my opinion. He's just an incredibly sweet caring guy.
Also, him bringing up that watchword is not the final scene with him
There are at least two more. Keep talking to him; I promise you it will be worth it. The final scene almost made my teeth rot out with how cute it was.
Edit: typos