Separated for four years and neither of them will become interested in someone else in the meantime? I suppose it's possible. Oh, sure, they'll keep in touch via modern technology for a while, but as the days, weeks and months go by, they will be in contact less and less until one day they'll realize they haven't contacted each other in well over a month. The bonds that have held them together will slip away and they will become, once again, nothing more than strangers.