I believe that trust is more important than happiness in a relationship. With out trust there will be no happiness, if you are insecure about the person you are in a relationship with, they will not be happy. They will feel locked down and feel like they are more in jail than in a relationship. Trust is somethng both people need in order for the relationship to succeed. If there is no trust than the relationship will fall apart because one person will always accuse the other person of doing something or think they are always lying to them.
You can't be happy if you have no trust. If there is no trust in the relationship one person always doubts the other and becomes over protective and annoying. When this starts to happen the other person who is not trusted feels betrayed and starts to become unhappy. Of course happiness is important in a relationship i agree with you there, just trust is a lot more important