Is is ok to be super worried about my brother's lack of ambition in life?

It's been 5 years since his HS girlfriend passed away. He was 17 at the time and he remains single till this day.

I hate to see him like this. Certain days, he acts distant. He's a shell of his former self. Is he going to date again? He was so brilliant before, a smart student with a promising future (high grades and scores), creative in many areas and an overall dynamic person.

His lack of ambition and enthusiasm in life worries me. He's also not even trying to hit on any girl either. I'm serious. Even if I were to present a pretty girl right in his face, he'll ignore it. It seems as if he's not progressing and has shut down in life. That event still haunts him.

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She was his first girlfriend, his first love and once in a while I'm told by my parents that he has nightmares about the accident.
His friend was the drive, his car got greatly impacted. Both survived with moderate injuries except her. She died instantly.
Is is ok to be super worried about my brother's lack of ambition in life?
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