Hey, welcome to the forum!
I have a few thoughts for you
First of all, bunnies can’t ever really be bonded unless both are neutered, because the hormones lead them to act unpredictably and affects their temperament.
You can’t really stop him being territorial, bunnies will always be territorial. The way to avoid this during bonding is to bond in a neutral area, somewhere neither of them have been before. Lots of people try the bathroom, for instance!
If you don’t have any neutral areas, you can try and create one by cleaning it with vinegar to eliminate the smell.
Overall, I’d say it’s a really great sign that they like each other, and that he’s fairly willing to let her near his territory, I think when you try to bond them it will probably be a match made in heaven!
However, until she’s neutered you can’t trust them together, so I’d wait until she’s been fixed, and then do some bonding in neutral territory.