Trust,commitment and communication are the three pillars of a relationship.

Trust is like paper..once crumpled it can never be perfect again.So never break it.It's very hard for a relationship to sustain itself once trust issues start creeping in.
Commitment is crucial.It is important that you are committed to the relationship and from time to time keep showing this to your partner.
Communication is often undervalued.It is of paramount importance and lack of it is often one of the major reasons for relationships falling out.Whenever you have an issue or there is something that is bothering you..talk it out with your partner..don't keep it concealed within you..he should know what you feel about him and the relationship.