xion it's just a girl. don't kill urself over something so dumb.
First let me say, I agree with Zooman's ultimate conclusion: DON'T KILL YOURSELF, PLEASE!
Otherwise, I would try to refrain from calling what he is upset about "dumb." Emotions are tough things to understand, read, and cope with. While it may seem silly to someone else, or even to Xion himself in the future, right now, it certainly isn't. Furthermore, he linked his depression to SA, not specifically this interaction with the girl. For all we know, this could be one of many negative experiences he's had. As cheesy as this sounds, calling his feelings dumb trivializes his experience and feelings of discontent.
That being said, killing yourself
is dumb. Don't do that. What may seem unbearable now, may not be in the future. You owe it to yourself to accrue more experience before you do anything drastic.