:/.
Boar trio's rarely work, even when brought up together from birth, I would also never add another boar to an already bonded pair as this can fluff up their bond. And you could have three single pigs. But I believe from the other thread I saw this morning, you was already given this information.
Sometimes it's better to have your original two pigs and learn with them before getting more, as now you will need to find him a friend now and dependent on his age and behaviour this could take a while.
Especially as if they get ill, can you afford the vet bills etc.?
And ensure they all have ample cage space, this new pig would also have to be quarantined first. It's 120 minimum for two.