They get along well as friends, but the feeling i get from them is that they're always not fully comfortable romantically with each other, like they always have to make great efforts to keep the relationship going. It may be a bit tiresome for them to do that constantly.
There's no easy way out of a situation like that, i guess. One of them has to gather the courage and just admit things for themselves and the other. No cheating or betraying each other's trust, just be sincere about things. If everything goes well, they can maintain their friendship.