Just to put that out there, I've actually used the tactic of making pacts with people on night 1 before, in previous Mafia games, when I was a good guy, so it was really just a coincidence that I was a vampire this time around. And I've never broken one.
My fatal mistake was mentioning it in public. Especially since there were so many newbies who would immediately jump on it as a sign of suspicious activity. >_o