Sure, people make mistakes. Like accidentally leaving a piece of colored laundry in with the whites. Or forgetting to buy eggs with the rest of the groceries. Cheating, on the other hand, is a pretty good indication of a lack of maturity, respect, and trustworthiness. Can a cheater change? Unlikely. It's just a matter of temptation and opportunity. Everybody lies, but betraying the trust of someone you supposedly care about and who I assume cares about you is a transgression I find particularly egregious.
In answer to your questions:
1: Have you ever cheated on your girlfriend/boyfriend - Wife/Husband? No
2: If you did, was it a simple kiss? more? N/A
3: Did you tell them you did?, did he/she forgive you? N/A
4: Are you trying to find an excuse, (as in "I was drunk", "Men/women have needs!") Or do you accept you made a mistake and regret it? N/A
5: Has someone cheated on you? Did you forgive them? Yes. In a way I've forgiven her, but it was in order for me to move on not to repair any type of friendship. I'm not angry with her anymore and don't bear her any ill will, but I certainly lost a lot of respect for her.
6: If you started a relationship with someone. Or knew that he/she had cheated on someone before going out with them, would you break up/not go out with them? Probably would not continue that relationship.
7: If you know a person who has cheated. (Cheated = always a cheater) Will you always think of that person as that? And never forgive their mistake. If so, why? (explain) Forgive, but not forget.