Trust is definitely essential for involvement on a relationship aspect. However, most relationships have very little trust in them.
That is why you see women prying into mens personal space in search or a clue. Or men checking or rambling through a woman's purse just to see if he finds anything out the ordinary.
Women who feel the need to stay in constant contact with their man throughout the day, have a lack of trust in him... by calling or communicating daily and often during that day, you are essentially trying to keep his mind on you, and at the same time trying to see what it is he is doing while the two of you are apart.

These are all normal things in most relationships, however, most often these relationships don't last. And if they do fall into years, it's only because one or the other hasn't been caught prying yet.

My opinion of this has always been firm. In order to achieve a harmonious relationship with any individual, you must establish a friendship. A friendship built on trust and honesty. We often say those are 2 of the key ingredients that we look for in a mate, however, we are very quick to sacrifice those for someone we are physically, or lustfully attracted to.

When you sacrifice those 2 qualities, you come into the relationship in fear. Fear causes you to snoop, question different actions, wonder different scenarios, thus, beginning to pry into areas of their lives in order to see if you missed anything.

And often times, when you snoop, you pretty much find. (I've always believed that. When you are looking for something, you're looking to find it, therefore, you will search and search until you do. And sometimes it's your own imagination that causes you to find something that isn't there.) You react off of your findings, in the interim you lose the relationship, why?

Due to a lack of trust.

And that's just one case scenario where the lack of trust causes relationship issues, and insecurities.

Always, always get to know the person you are dating. It is very important to do this before you allow yourself to fall heavily into infatuation, and lust. Then those two things will cloud your judgment, and because you don't really know the person you are with, you begin to do things in search of clues, and often times, like I said, you find them.
Your feelings are deeply wounded, but it could have all been alleviated if you had taken the time from the start to develop a friendship and a trust.