Some things to think about:
Neutering can be risky unless you have a very competent vet who is used to doing this op on piggies
And (so I've read, no personal experience), not all boars and sows necessarily get on.
But, in favour of neutering and pairing him with a sow - IF - you have a good vet - is that you can take him to choose his new girlfriend and be pretty sure that if they take to each other they will not later fall out.
If you don't want to risk neutering, then pairing with a baby boar is often recommended as the easiest option because the baby will accept the adult as boss. BUT - as the baby grows up, he may launch a challenge and they could end up falling out.
Pairing adult boars requires time and patience, but if it works out, then you can get a really strong friendship. Because all the dominance issues are addressed at the beginning of the realtionship, once they have gotten past that stage, then you are less likely to get a falling-out at a later date.
It really depends on personality. Two very feisty boars will be constantly rivalling each other for dominance (like my Tom and Jez!) but if you get one very dominant boar and one submissive one, the submissive one may be bullied.
A feisty young adult may settle best with a more tolerant and laid-back older boar, like my feisty young Roo and older laid-back Sam.
Hope that is some help!
P.S. Are you absolutely sure yours are not getting on? As it's the weekend now, could you possibly keep a very close eye on them during the next 48 hours and see what's going on/ maybe even have them in your room overnight? - before assuming the worst and separating.