Okay here's one big mistake I made: I was not specific enough in my line of questioning and was deceived rather cleverly.
My first big relationship, lasted over a year, was pretty intense, suddenly started getting rather weird. My tomboy naturally so beautiful girlfriend suddenly started wearing makeup and suddenly her outings with a girlfriend or two seemed more important than my plans and I began to suspect she was seeing someone else.
So after some circuitous verbal maneuvering that wasn't very successful I did confront her and asked her if she was seeing another guy.
Well, she was very very convincing and I believed truthful in her denial, and became fairly attentive to me for a spell and I was lulled into a brief lack of suspicion. See she was being truthful. . . because she was seeing another woman! Within a month she had moved out and on to that relationship (and a series of others for quite soem time).