If the person indeed must stop going to that site, is obligated to stop talking to the people he met (through a medium which is not affiliated with that site) from that site? I ask this because the person should be sorry for lying, I assume (if this is really lying and a sin), so would that require him to wish he never lied and act as if he never did by not being able to talk to these people he met?
On the other hand, could he be sorry simply that he lied (if this is really lying) to meet these people and then still talk to them, because actually meeting them is not wrong but the wrong, if there is one, only comes from the lying, if it is lying? The issue is because it would be very difficult to have met the people without joining the site and checking the box to confirm age.