Killing himself is his choice and it isn't part of the rules of his religion (if it was then if that's what he truly wants to do we should accept that). Usually Christianity focuses more on overcoming sinful thoughts and feelings instead of destroying them by destroying yourself. If he truly was a highly Christian person he'd be trying to overcome his sins instead of killing himself to stop sinning. Unless you're trying to protect and save other people (like in a war) killing people is always a sin according to Christianity.