I don’t believe either one of you is a paranoid schizophrenic, so neither one of you have to worry about becoming a Seung-Hui Cho.
Even if you were ill, only an infinitesimal small percentage of the mentally ill kill.
If your friends think you are capable of this, change friends.

But Dave, there are a lot more differences between you and that guy in Virginia than you might think. I’ve been bullied as a kid, felt leftout & weird as a teenager, and had problems figuring out women (I’m married, but still working on that last one 😉 But there’s got to be something deeper that drives someone to murder – otherwise they’d be locking up every introspective geek in the country*. So give yourself some extra credit, you deserve it 🙂

*Note: I’ll even admit that this was one of the first thoughts I had once we got some bare details of the situation. "Oh no, they’re gonna start blaming ‘loners’ again – like every introspective, abused geek out there is a vial of nitroglycerine waiting to be pushed off the table." It’s a shallow bit of "insight" that’s easy for media types to trot out.

Problem is that it’s a bunch of fallacious nonsense.