You stated that the bike charged fine at 14.5 volts to your friends house then you had to boost it and on the way home it was below 12.3 volts.
Sure does point to a battery. If the bike charged well to your friends house, it should have had the capacity to start the bike. On the way home, you couldn't charge the battery. Take the battery to an approved auto pro shop and have it tested. Sounds like it has no capacity and shorts out at times.
There are other things that could cause the problem from a faulty ignition switch to a poor ground or power lead. Since the ground was checked, make sure the hidden connections under the seat are not at fault.
