Yes, if one is male and the other is female, at some point the male will pursue the female to try to mate. This will cause stress to the female if he's constantly harassing her.
It's best to keep tortoises separate and not to keep them together in pairs. They may seem like they get along to us, but because they're so territorial, they're constantly stressed out. One will always become dominant over the other and you'll end up with one healthy tort and the other will be small and/or sickly.