It's very difficult with boars Louis tbh. It entirely depends on their characters.
With boar pairings (which contrary to popular belief, can be very succesful) you will always get one dominant boar. The question is finding a boar who will submit to the other one and be happy with that. If you get two boars who want to be dominant, you will get a little of squabbling and most of the time they will need to live in separate cages - like our two. This is still better than having just one piggy as they talk to each other through their cages and are happy that another piggy is around.
Age is another factor. This could be a loooong post so I'll try to stick to the main points. At around 3-5 months old, boars enter "pubity" essnetially and testosterone starts to run amock in their bodies. This can continue right up until full maturity at 14 months old. During this period, they will be aggressive and stroppy with any other boar - even if they had previously good relationships. This might not lead to separation if the bickering doesn;t end in full-on fighting with biting and scratching. If this does happen, you will need to separate them. You might eventually be able to reintroduce them at a later stage but this is quite rare.
If you have an older boar and a younger boar together with a reasonable age gap, you might have a better chance of success as the older boar could be protective and fatherly to the younger one. There's a trick to introducing them but that takes a few lines to explain.
Finally, if you want to get another boar of the same age, you will need to keep them apart to begin with and introduce them to each other on "neutral" ground. If they get on, they may be able to live together but you will need to clean the cage thoroughly beforehand and make sure you have two of everything (water bottle, hay feeder, treat/veg bowl etc.) that way they won;t get territorial.
You may want to think about neutering your boar at a later stage (but before he reaches 1 year old) and then you can pair him with a sow (female piggy) which is often more succesful.
Let me know how it goes please - oh and what's piggy's name and do you have pics?