Sarah is correct in saying the reason why you cannot bond them and why you cannot attempt to bond them at this time is because they are not both spayed. Rabbits who are not spayed/neutered are driven by their hormones to defend their territory, so it is very dangerous to have two rabbits together, whether it be supervised or not, since chasing and biting, as you mention, occur very suddenly. Until they are both spayed and have had at least a month to settle after the spay operation (for recovery and hormone regulation), they need to stay separated, especially since they have already fought. Rabbits can hold grudges, so they need to forget each other until they are both fixed and ready to go through bonding.
In terms of Mochi specifically, her territorial behavior may be because of her hormones and not being spayed. Acts of aggression dealing with her space will most likely lessen when she is spayed.
As Sarah mentioned as well, a rabbit not “kissing” or cuddling is common, and between having fits with Mochi and being still new to you, it is not surprising that she is not yet relaxed and trusting. It is not an attribution of breed necessarily. Both you and your boyfriend interact with the rabbits differently, in nuanced ways, so perhaps ask your boyfriend how he interacts with them both. On one hand, if you’re the only one that attempts “bonding” them and he does not, that is a major flag that being in an environment that harbors those fighting memories is inherently uncomfortable and she’s reluctant to relax.
The next step is separation until they are fixed, then you can try to bond them over several months (it is a long process). I recommend reading the bonding info provided by this website to you know what to expect when the time comes: https://binkybunny.com/BUNNYINFO/tabid/53/CategoryID/9/PID/940/Default.aspx
Also note that the presence of an unfixed rabbit can stir hormonal behaviors from a fixed one, so it’s recommended for both to be fixed.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.