When closing up and dealing with all this drama I'd been in, I at least was able to find and put into words my motto for my beliefs in how I interact with people guy or girl, friend or acquaintance in terms of trust:
I'll give advice, believe in them, and let their actions speak for themselves.
If they fuck me over, or do something really messed up, I'll walk. No bargaining, no bickering. Just be supportive and let people make their own choices and represent themselves.
As opposed to telling them what to do, and threatening them that if they don't do it, I'll walk.
People always tell me that I'm too nice (not like girls saying "nice guy", but like guy friends telling me I'm too trusting and supportive), but no matter how many times I get burned, I still like to believe that people are generally good at their core and everyone makes mistakes. I'd rather assume someone is a decent human being and get burned than watch my back and never fully trust them. The latter just seems like the whole "state of fear" lifestyle.