My experiences with relationships are overwhelmingly positive. However, there's always a non-zero risk that such a maneuver can happen. I've seen it happen, many times. Even in otherwise happy couples. Are you willing to bet your future on it?
I guess. I've never had reason not to be open about these issues and it's never disrupted trust in the relationship. I've discussed these ideas with every partner I've ever had. They weren't offended, they understood. Many even had their own stories of unplanned pregnancies to share.
My girlfriend lets me give her the trimestral birth control injections.