Fan Casting She is All Grown Up in Sort by Tropes

So this guy hasn't seen his Childhood Friend in a long time. Then they meet again, and she's absolutely stunning. He realizes that his friend that he never thought of in "that way" really can be thought of in that way, usually just as she starts dating someone else. If he pairs up with her in the end, it will invariably be revealed that she had been in love with him all along; she just needed time to mature (and maybe switch to contacts) before she could catch his eye.