What do you do when they lie from day one?

I recently came from a 15 month relationship that was literally built on a lie.  From the first conversation we had to the day we ended. How do you begin to trust again when you have no way to know that some people are just born liars? When I started to have serious doubts I started digging – now I am not proud but my ex-husband LOVED to have affairs that I discovered by being doubtful so I learned how to shall we say find “creative” ways to access emails etc. So when I started feeling that same odd “hmmmm” feeling I started digging. And sure enough not only was he seeing someone else on me but I guess he was still living with his wife when we met!  She moved out 2 weeks after we met. Of course I had been told she had been gone for months blah blah blah. Oh yeah and the divorce that he said was final – it wasn’t those cases are public and can be searched on court records in that state. But he also had an affair on her as well.

He even had his 16 year old daughter lie to me!  How horrible is that???

So my question I guess I am posing to the general forum – is how do you know? I mean I have a friend in the secret service do I have them run every guy I date? Why do men (in my case – I know women do as well) feel the need to lie from day one when at that point you honestly have given them no reason to. I was taught to always be open, up front and honest – no matter how good or bad a situation is so I take that with me to other relationships and try to be as honest as possible.

Are there really any good men left over the age of 40 that want an honest sincere relationship or all my guy friends telling it straight when they say all men that age want is sex and if they can get more than one woman all the better!