Having a very tough time bonding, advice greatly appreciated!

I apologize in advance that this is long I just want to include all information and I'm at a loss for what to do next.

So I've had my female bun Tater for about 6 months now, she's 8 months old and spayed. I really wanted to get her a friend as I know how beneficial it is for bunnies.

I adopted a male bunny the same age as her, Gravy (also fixed) from a bunny rescue. When I went to pick him up his foster mom informed me that he was bullied by his brothers and mother and actually had suffered a very bad bite on his butt from his brother (I can still feel the bump). This wasn't mentioned at all beforehand until he was being handed to me in his carrier.

He is the sweetest little bun and so tiny, he is the runt of the litter and I'm still not quite over how small he really is. The thing is he is only sweet with humans. Otherwise he is super aggressive. He goes after my cat (doesn't bite her but lunges and growls, my cat is fine with Tater and him). But the real issue is he's SUPER aggressive with Tater. Their first bonding session went great, he was grooming her and there was no aggression. But as the sessions have went on it just results in full on fights 90% of the time him instigating.

I've tried so many things. I've swapped toys and litters. I've even swapped them into their different enclosures (both free roam, he's in my bedroom and she gets the living room, they are sectioned off by a baby gate). I swap little stuffed bunnies they both have and when I do they both groom the stuffed bunnies, no aggression towards them. After a particularly nasty fight I decided to break off the dates and kept them seperate completely for two weeks while still swapping enclosures. Tried another date and it's the same situation.

I can't even have him out in the living room in an x-pen because she tries to sniff him and he just attacks her through the bars. Ive tried dates in a small neutral territory (bathroom) and a larger neutral territory (spare room) I've tried stress bonding in the carrier which honestly scares tater so much it kinda breaks my heart, but the dates are calm after those for about 10 minutes before he's back at it again. It makes no difference, he instantly attacks and it's aggressive. I always give a treat at the beginning of the date and try to end on a good note (which is not easy due to all of the above).

It's just difficult to know what to do. How much fighting do I let happen? I've read so many different things. Some say to leave them to sort it out and interfere as little as possible, some say stop fighting instantly. The thing is if I'm to stop fighting instantly I can't even let them near eachother because it's an instant fight. Ive noticed small scratches on Tater and I want this to work out but I just feel so bad doing this to her (no bleeding and they're tiny but still). It started out so great I don't know where it went wrong. I can tell she wants to get a long with him but he's just not having it.

Is this hopeless? I'm so attached to him and with his past I want him to have a chance to bond (the rescue will gladly take him back if they are unable to bond no issues and my ultimate goal is to find tater a friend as I can tell she's a bunny who would benefit greatly from one). The rescue said he needed to be adopted to a home with a bunny for him to bond with but I'm wondering if due to the trauma he had if he's better as a single bun? Is there any way to help him get past this?

Everytime I look up bonding videos/advice the bunnies always look so chill and there's no fighting so I can't even tell if this is normal/really bad etc. Does anyone have any experience bonding a difficult pair where there's been legit fights? I've even looked into shelters that do bonding for you/come give you advice but as I'm in Ontario I can't seem to find anything like that available.

Any advice at all is welcome but I'm really hoping someone with a similar experience can let me know what worked for them (or if it just can't work).

Don't beat yourself up over it. Some rabbits simply refuse to get along with another particular rabbit. It is just the way they are. Some are more choosey than others. It doesn't mean you did anything wrong.

I have had easy bonds and I have had impossible attempts of bonds. I know there are some that will persist at a difficult bond for months and months. I don't agree with that. In my mind, there comes a point when at least one rabbit is simply being unduly stressed for too long over the whole process.

There is nothing wrong with trading the new guy in for another. I know it's easy to feel guilty, but it likely will turn out better for both rabbits. They each can get a chance at a more compatible bondmate.

The bond attempts I had that did not work out, had started out on a decent note but got progressively worse as time went on. I wanted so much for the bond to work, that it took me a bit to look back objectively and admit that things had been getting worse - not improving. Ultimately, it was definitely worth it, in my book, to have gone ahead and exchanged the new rabbit for another. I was stressed before that and I know both rabbits were as well. If you have been stressed too, try to relax if you do get a new bun, and not let your stress (fear of them not getting along) pass on to them.