Okay, here’s a little background info with my two buns, Pongo & Gizmo:
About a year & a half ago my mother, sister & I went up to Tennessee to get a rabbit. Well, we ended up getting two little baby boys(brothers) & on the drive home my sister fell in love with one(Gizmo) so she ended up keeping him while I kept Pongo. A couple months ago we ended up moving Gizmo in so he could get a little more attention, seeing as how im still in high school & have nothing better to do
So they have both been in separate cages in my room, but I’ve been trying to bond them so I can someday put them together. Usually when they run around they are separated by a fence, but they’ll lay next to each other & groom each other through the fence. I started putting them together in a small area after they got to know each other through the fence about a month or so ago & it’s been smooth sailing; no problems with fighting…minimal mounting, it’s really been great 
But today I had them together after a couple days apart & I guess Gizmo was grumpy from being stuck in his cage because he started mounting Pongo as soon as they were together. Pongo tends to let him for a second & then I will remove him, but Gizmo was being unusually aggressive, which obviously made Pongo uncomfortable. So, they started going in circles & I intervened but Gizmo had managed to bite Pongo(& me) & held on for a second
I put Giz in his cage & checked Pongo out. He seems to be okay & I dont see blood or fur missing. I put the fence back up & they’ve been laying beside each other like normal but there’s a little uneasiness.
So, I guess I’d just like some advice on where to go from here. Should I keep the fence until they seem okay again? & a question on grooming: Gizmo grooms Pongo a lot, but sometimes it seems a little aggressive. I read that it does often look like they’re kind of nibbling, but how can I tell when the grooming does get to be too much?
Thanks for all the help, sorry about all the typing 