I find it very hard to let go of certain piggies sometimes, so I can totally empathise! ;D
I think maybe if he cant be bonded with another boar, it would be better to keep him on his own giving him lots and lots of attention until he is old enough to get neutered and then get him a girlfriend.
You know your own guinea, and its better for him to stay on his own, be handled very regularly by you and become more and more tame, rather than you constantly worrying about trying to introduce him to other boars, and those bad experiences wil probably affect his behaviour with other guineas when hes older..
When hes less scared and more settled, he's going to be less likely to bite....and putting him in with other boars, which you have established he does not like...is only going to make him more aggressive imo.
I know people will disagree, but if he carries on this way, like i say, i think it would be best to keep him on his own with a lot of attention from you until he's old enough to be neutered...then take him to a rescue and let him have a sniff around the ladies (which most rescues will allow) and he can choose which he likes, and which sow is compatable and isnt going to cause a problem!
Obviously its up to you, but bear in mind he hasnt even gone through his 'teenage' stage yet...and thats when the poop usually hits the fan...so at least if hes neutered you have a back up plan in case its not possible for him to live with a boar in the future!