Your comment is debatable.
In my opinion, it is not as much as, is it the boy or the girl the first one to forget their first love, but various factors like, personality/attitude/nature of relationship the two shared/family background/religious beliefs/personal experiences dealing with relationships of various kinds, to name a few goes on to show how people deal with relationships, or how they move on from relationships. Gender is not one of the very important factors here.
However, first love is dear to all. It would not be something that one could forget easily.
If there is something more specific to your experience, you could share here, and we will try to guide you appropriately. You could also come online for an interactive chat where you could address this or any other issue, to gain a more personal insight into your concerns.