Because like Raspberry said above, he might love his future wife, and he might be getting married for whatever reasons, but that doesn't always carry through to his actions. A lot of men have a difficult time cutting loose the OGs and focusing on his new wife. This is not a unique situation. Women, however, sometimes act brand new and want to keep living the fantasy--"well if he REALLY loved her/wants to be with her, why does he keep calling me?"
He keeps calling you because he wants to keep all his options open for as long as the other women in his life will let him do so. He "should" be man enough to be 100% abt his new relationship. But just because he's failing to do the right thing, you, nor anyone else, has to be complicit in it.