What breed are they? A lot of people run mixed groups together to this age with no problem. By the time they are showing interest they are off to the freezer. However, if you find the gilt coming into season and the boar taking interest sooner you might have to separate but to be honest I am sure lots of gilts go to slaughter already "caught".
With only two pigs separating is likely to cause stress unless you can do it so they can still see each other.