Yes, if she rejects him based on this, next time he won't tell the person he is dating. He may be forced to lie to keep dating. But is that really your problem?

The fact that he murdered his parents must mean he is completely ****ed up. Those people raised him and learned him all his basic abilities. Be it restraint, moral compass, how to get in an argument and how to resolve it, responsibilities, etc etc.

I find it strange that people bring up that one should ignore the law and follow your own instincts. What does the law have to do with this? You can get in a fight with an equal, where both agree to fight, and illegally kill someone and get a murder conviction. Or murder someone for a greater good. But this person murdered his parents.

And I wouldn't worry about him being lonely forever. There is going to be someone else attracted by his ****ed-up-ness.

Find someone boring instead.