Man, I only wish I had someone telling me I was bad in bed, back in the day. I was none too great apparently and it took until my 3rd girlfriend until she said "As well as your self loathing and insecurities, you're not the best in bed...at all...actually"
So I worked on it, thanks to the feedback and haven't had any complaints. I think if your gonna engage in a relationship you should be honest about that kind of thing. Sex is a large part of a happy and healthy relationship and in my experience, things are always fixable. There's always room for improvement from both sides.