Trust your gut instinct. It has always worked for you. And you have always regretted the times you did not trust it.
People lie. All the time. through their teeth. And people are also very capable of coming up with explanations to explain away every lie. Not. worth. anything.
Desist from painting everyone with a wide brush. It's most easy to give in to, but you know it doesn't paint the correct picture.
It's never too late to admit that you were stupid/foolish/got taken for a ride. And no one is infallible, so its ok if you did. The important thing is to stop denying it, be able to face it and remember the lessons you learned from it.
Sometimes I can't stop wondering Why? Why me? How me? But when I step back and take it all in, it just makes me laugh. :)