Help with relationships with people who don’t tell the truth and are secretive/deceptive.

I am challenged working with the model and my thoughts/perceptions regarding people I’m in relationship with who do not tell the truth. While I certainly have my thoughts and feelings about interacting with people who aren’t truthful, it also seems as though their behavior is actually the circumstance since they admittedly are deceptive with others too…this is simply how they choose to be (which is certainly up to them). It would seem reasonable for me to verbalize and set a boundary with them regarding me not participating with them if they aren’t telling the truth, but I can’t always know whether they are or they aren’t, so it’s a bit of a dilemma for me! Any and all assistance is welcomed… 🙂