Hi and welcome
Good that you are asking before you are acting!
Any full boar over 3 weeks is a big no no around sows. The ladies are nonstop breeding machines which come into season again within hours of giving birth until they die giving birth or their bodies give out. Guinea pigs start procreating as soon as they are weaned and there is no menopause. I know of a 9 years old sow becoming pregnant when put with a boar during a holiday - needless to say that it didn't end well.
About every 5th birth ends with the death of babies and/or the mother - and that is the best case scenario. Biology is brutal for guinea pigs. It is the price they pay for having (together with their larger swamp cousins, the capybaras) the largest and most developed babies of all rodents, which are able to follow the group and survive on their own just a day or two after birth.
You cannot just take the boar out every few days because that will seriously destabilise the bond. If a season happens overnight or spontaneously during the introduction, you have had it because the act itself takes just seconds and you cannot get at them that quickly. It is not a matter of whether it happens, it will be a matter of how soon it is going to happen.
It is all even more complicated because not sexual mounting is also a normal daily dominance behaviour for some boars (and is in this context also occasionally used by sows, especially sows in season).
I have adopted plenty of piggies from uncontrolled procreating situations backgrounds (hoarding) where things quickly got out of hand once the babies got going. It is one of the reasons why we have a strict no intentional breeding/putting mixed genders together without one party being safely de-sexed.
The best way forward for you is to keep your boy in an adjoining cage for the time being with interaction through the bars while making sure that he cannot climb/jump across he divider/cage or wiggle loose any grids in order to get a sow in season. Please cable-tie all adjoining grids and peg a sheet over the top of the boy's pen along the divider so that he cannot get over the top.
For the longer term you might want consider neutering. Please note that a single boar can live alongside sows but not most bonded boars unless you want to risk fall-outs.
Neutered / De-sexed Boars And Neutering Operations: Myths, Facts and Post-op Care