Honesty is the best policy in relationships.
If you are romantically involved with someone, honesty is the most important aspect of a relationship. Honesty does not just include where you are and who you talk to; it goes much deeper than that.
First off, you must be honest with yourself in what you are looking for in a relationship. You know who you are attracted to, what type of person you want to be with and what kind of relationship you are looking for. Never short change yourself relationship wise just because your significant other is extremely attractive. This also means that you should not carry on in a relationship that you do not want. This will only hurt both of you in the long run.
Honesty also goes into marriage. You must be honest with your spouse about your future plans. This may include children, living location, jobs, financial records etc. With honesty come respect, love and most importantly trust.