My husband’s best friend recently told me about something my husband had done when we were dating, and it involved flirting with a common friend. I asked my husband about it, and he dismissed it, saying it happened a long time ago. I didn’t react but have been thinking about that a lot because it implies that he didn’t take me seriously back then. If he could flirt with another woman and not say anything about it for years, I don’t know if he has done this after we got married. We have been married for three years now and I am worried about whether he may change in the years to come and revert to that kind of behaviour. Am I right to be concerned?
You should rely upon actions rather than words, consider why the two of you decided to marry, and evaluate what keeps you together. Talking about this is great, because it allows you both to hear the other person’s side, but the rest is all speculative because he hasn’t done anything to give you any cause for concern. We can’t predict how relationships evolve, or break down, but what we can do is focus on the present and do everything we can to make sure the bond is strong. Talk about your fears, tell your husband why you are concerned, and commit towards working together and strengthening your relationship. That is all anyone can hope for.

Should I tell my best friend that I am thinking about dating a guy she absolutely despises? It may make sense to tell her later, but she may not understand my reasons. What should I do?
This depends upon what her reasons are, what your reasons are, and why you put so little faith in her ability to see things from your perspective. The sooner you discuss this, the easier it will be for you both to come to terms with it. Listen to what she has to say because she has your best interests at heart.