Amnesia - Is it possible to remember everyone but to forget only one person?

I'm really interested in this thing:
Is it possible to remember your parents, brothers, almost about everything but to forget only one person? Imagine this story:
This guy who's very good with fire weapons and martial arts is fighting with his enemy and his men.
After the fight with an army of maybe 5-600 hundred people and protecting his family, he's starting to feel exhausted because he's trying to protect his family members but not himself too.
And then he get shout in the right side of his abdomen but still fighting. After dealing with all that people he's falling down on his knees cause of the pain in his abdomen and when he was falling he had hit his head. When he'll wake up in the hospital he will remember everything until the day when the fight was and the most important he won't remember his girlfriend like she was never part of his life. (he loves her truly and she's the love of his life but his girlfriend is his enemy's daughter)
So my question is: Is it possible to remember everyone but to forget only one person?
Can your brain protect himself from the pain and forget a certain person? (because if he remembered her he wouldn't be with her even if he loves her that much just because of the blood she carries inside in her) Can you loose your memory about somebody due to depression?
And if you remember would you be depressed if you can't have a certain someone?

If the memory loss was due to a physical injury to his brain, he would likely either remember or forget all of the people that he dealt with in the same period of time but it's doubtful it would be selective. Sometimes people can not remember what happened recently but can remember their childhood for example.

We can also block memories of painful experiences and that can be selective. If, while scanning the horizon with the scope on his sniper's rifle looking for the remaining members of the army he wiped out, he spotted his brother kissing the girl he loves, that might give him reason to block her from his memory not to mention what he might do to his brother.

After killing 600 enemy soldiers, getting shot in the belly and seeing your good-for-nothing brother taking advantage of your absence, that would surely qualify as a depressing day in my mind.