A large part of trust issues or jealousy are based upon past bad experiences in other relationships or having the "feeling" (you love your mate more than she/he loves you).
Very often there are issues with (expectations) of how one person feels their mate "should" behave or think if they are "truly in love" with them. For instance one person may think if you love me then you would not (need) to have a "girls night/getaway" or "boys night/getaway". Another example may be one partner believes you should not remain friends with exes while the other person sees no problem with it.
The bottom line is there really is no "right" or "wrong" in relationships. There is only "agree" or "disagree". Ultimately we are all looking for someone who (naturally agrees) with us on the important things in life and (wants the same things) for the relationship/marriage.
If you are "madly in love" with someone you want to (reassure) them that they have your heart and you would never do anything to intentionally hurt them.
Sometimes giving them a little more attention, leaving love notes on the mirror, sending them an email or leaving a voice mail telling them how much you love or miss them. Women that initiate sex more often make their men feel "desired". Men who come up with suprise creative romantic ideas can make women feel "appreciated/loved". These are things people (naturally) do when they first fall in love with one another. Over the years they often let things slide. If you are with a natural "romantic" she or he may view this change as being a sign that there is a lack of interest or you no longer feel the way you once did about them. A wife/husband wants to know and (feel) "special". I recently wrote a hub to help the "romantically challenged" stay on track with (nurturing) their relationships. http://hubpages.com/relationships/SecretLoversCale...