Hi, you did very well to separate them when signs of aggression were shown.
@sport_billy gave fantastic advise on trying to neutralize behavior and biting. We have been working for about 8 months now on our first guinea pig rescue, whom is a very dominant personality (I just got a couple stitches from trying to intervene the last failed bonding-totally my fault and haven't had the problem of hard nips again). While I am still learning a lot, especially with boars, I have noticed with our very stubborn little Tybalt that changes can affect him as well and when he is in a mode to be more scared or uncertain, he responds to the end fighting and in more ways then just the biting. Even changing a short time with bonding and changing the cages around to where the boars and even the female cages, at one point, seemed to give him more stress and he began shaking and biting the cages. Yep, our little monster :-).
It really sounds as if you have a bit of stressed and uncertain little guy there. This is really going to take some time, he even has to get used to being separated from the other two now. I know it's rare a guinea pig can't bond with another after some work, our Tybalt seems to be unable to be bonded at this stage successfully with another and he is alone as well. We have first put the two cavy cages back to back with another male whom we are bonding in the very near future and waited some days for the two boars to settle down before taking the back walls apart and connecting the cage so that there is just one wall as a separator between the two. They are not chattering anymore and are sniffing noses through the openings of the separator.
These guys are with my 17 year old daughter in her room. She is in there a lot and gives them a lot of one on one time most of the day so they do get attention from her and myself (she will take them each out to bring down to see me or we will go outside and they are there an hour or two in the outdoor run we made for them). We do this with each one. However, they are still quite lonely at times during the day, even with us there. I am still unsure what we will do with Tybalt as we have even had females with him (he was a 'she' when we rescued him, we found out he is a neutered male later on) and he is simply too aggressive. Our other boar is not so aggressive and was bullied by Tybalt. He won't be alone long as he does need a friend.
If you can maybe give him some time and attention and with a little patience, maybe in the future piggy dating can be an option or possibly neutering and having a female companion, when you are both ready to try . I think in this situation, it may just take some time and care in earning his trust.