Two things:
Lying and leaving. I don't deal with either very well. I have ceased communication with someone extremely dear to me who lied to me once. Big, bad lie. Time passed, things were addressed and truth was told, and now we're good and I don't even think about it unless something like this is mentioned.
Leaving --- since 1973, leaving is the ultimate deal-breaker for me. If you are a loved one of mine and you turn your back on me, (and this is a character flaw, but I'm being honest) you may as well be dead to me because I will do absolutely nothing to help you, I will not talk with or hear you, and you become my enemy. I'm fiercely loyal, but when I'm betrayed, that's all she wrote.
Human government bears the same relation to hell as the church bears to heaven. (David Lipscomb, On Civil Government, 72).