If he’s trying to mount her I’d keep them separated at least until after his neuter, if not also until after her spay. Once each has been neutered/spayed they will also require some time for any remaining hormones to settle down. They won’t have formed a proper bond yet, just a ‘baby bond’ which would likely break down as each hits puberty anyway, so to avoid unwanted pregnancy separating them is necessary.

Maybe in the meantime give Mochi some free roaming exercise time each day whilst Boba is shut in his enclosure so she isn’t always in the pen.

@amyef2000 covered it well, you need to keep them separated until spay and neuter.  Babies (which they are both definitely babies) do get along but do not truly bond, and the fact that you are seeing some mounting means that hormones are coming in. Both to avoid accidental pregnancies and injuries to your young Mochi.

Keeping them as neighbors means they will still enjoy each other’s company and will not forget each other, so don’t feel bad about that.

Boys can be neutered as early as their testicles drop (usually between 3-6 months), and females can be spayed at 4-6 months, depending on how large she is and what your vet recommends. After the procedures, you’ll want to wait for hormones to settle for a few weeks.

In the meantime, I really like using NIC cube grids and x-pen fencing to create temporary housing, or to divide up rooms for free-roam time. You’ll want to have the fence have a buffer of 6 inches to prevent nipping through the bars, which can happen suddenly. They can also mate through the bars…so having the buffer is important! Perhaps Mochi can have access to one room, and Boba can have the rest of the house. Or you could pen Boba part of the time and give them shifts of free roam time (like one gets the morning and other one gets the evening).

Firstly, if neither of them are not fixed, they should not be allowed to interact. Female rabbits can become pregnant as soon as 12 weeks old, and there’s probably some variation to that,  so to ensure you do not have a litter on your hands, they need to be separated. There needs to be a gap between them as well, as rabbits have been known to breed through a cage wall.

Whether or not they get along now may drastically change once they are old enough to be fixed. Baby bonds are not true, permanent bonds, so I wouldn’t be too concerned about doing permanent damage to a lifelong relationship because they are separated now. Once they are both fixed, then and only then can you begin to make some permanent progress to their lifelong relationship. Strides in a baby bond are temporary and typically unstable.

If you have not already, I recommend reading the bonding information in the RABBIT INFO section of this website!