Why lie? Act I

I figure there are two and a half major types of lying:

Type #1: Lying for the sake of the LIAR

Type #2: Lying for the sake of the INDIVIDUAL TO WHOM THE LIE IS TOLD

Type #2.5 Lying for the sake of a NON-PRESENT INDIVIDUAL

Now, there is a big umbrella with these categories:
It seems to me that most people think they are lying for the sake of another individual. How many of these people are really lying for the sake of his or herself?

The perfect example is the act of cheating on a partner. In this situation, the cheater often has the pressure of possibly ending what may be a desired relationship through telling the truth. I have discussed this issue with a small sample of transgressors; cheaters often express that they are doing their partner a favor by lying about their unfaithfulness. The cheater believes that they are type #2 lying; they are lying to not cause distress and pain to their partner. I believe* that in most situations these individuals are in actuality 'type #1 lying' by not admitting their exploit, and 'type #2' lying to their OWN SELF to believe that this is not in actuality a predominantly self-centered act. They are lying to avoid the pain of hurting the feelings of their partner, the guilt of their act, the possibility of 'breaking up', the possible loss of a best friend and/or sexual partner, etc. They are lying because it is EASIER to bear coping with the possibility of internal guilt for a single act than to weather with the consequences of the actions being known.

I tend to be fairly black and white when it comes to honesty. I do not believe in lying, and I do not do it without great reason (generally, the responsibility for someone outside of myself). However, I have not been able to logically understand why I feel this way.

Why does truth matter? There are countless situations in which not knowing the truth would save great distress. We have ideas of it being inherently "right" to be truthful, or that we "owe" it to others to be honest. However, confusingly, none of these strike me as being fully legitimate reasons. I cannot logically explain why I should be so polar on my feelings on lying.

In the earlier example, the cheater could possibly feel a level of self-sacrifice for bearing the guilt of their act and not telling their partner the truth. I cannot truly justify this as being wrong. I absolutely disagree with the sentiment, but I cannot explain why.

As a personal example, I once had a partner tell me, "If I ever got pregnant, I would just get an abortion and not tell you; I don't think you could handle it." This clearly sparked a discussion. But, was she right? In my opinion, absolutely not.

I know maxims are cliche, but I fully believe in the concept that "we are like photographs: we develop from the negatives." By lying to avoid and/or appease pain we are not only perpetrating a moral offense through the act, but we are enacting the greater misdeed of stifling the growth of each involved individual. Through dishonesty, we are stealing opportunities to increase the potential and capacity of experience.

There are many arguments at this point about which I do not have time to write. However, I just want to point out this is my personal philosophy, and I fully recognize that it may be mine alone. I do not believe that I am "more moral" or a "better person" for these personal rules. I find that understanding one's 'moral guidelines' is kind of like being vegan: by having specific rules it allows one to feel a greater level of independence and control.

*I am always open to the possibility of being swayed to another opinion, or simply changing my mind. My use of "blanket" or "black and white" statements should be read as "based on my experience thus far I choose to believe xyz until I discover or am convinced of otherwise"