What steps can I take to address my fears of bringing up concerns to my partner, given my previous relationship experiences?

What signs should you look for to know if you're using "it'll never work" as an excuse to avoid commitment?
What makes it so hard to see the manipulative nature of an affair at the time, and how can you gain clarity?
How can I differentiate between a minor issue and a potential deal-breaker in my relationship, especially when trust is involved?