From the wikipedofile:
Adultery (from Latin adulterium) is extramarital sex that is considered objectionable on social, religious, moral, or legal grounds. Although what sexual activities constitute adultery varies, as well as the social, religious, and legal consequences, the concept exists in many cultures and is similar in Christianity, Islam, and Judaism. A single act of sexual intercourse is generally sufficient to constitute adultery, and a more long-term sexual relationship is sometimes referred to as an affair.
Marital. Marriage. To be married.
Here in Canada, many people practice what is called common law marriage. It's generally a tax thing that the government uses to grab money from people living together for (I think) longer than 6 months. But, we also have (not sure the proper term of this) legal marriage. With that, you need to get a divorce after the seven year itch hits. (Seems to me that it's just a city politician and lawyer's scam to rake money in.)
Commitment to a partner, (marriage, business, or team sport), is just that: a commitment. I promise to... whatever, for however long, until something causes a uncommitment.
It has roots in religion. I am a-religious. Not atheistic, just not aligning myself with a religion philo-theo-sophy. I married my current wife (legally) to help her with immigration issues. We've been legally married for... ghod, let me count... eleven years, I think. Uh... November something, some year. Since I can't keep track of anniversaries, I'm sure I'm due for a divorce soon. Anyway, my previous marriage was a common law one and when the seven... wait, 8... year itch hit me, we didn't need a costly divorce (her and her current common law husband and I are all friends today!)
If I am going to play volleyball with a partner (or several), I am committed to play on their side and within their set of plans and agreements. Should I suddenly cross over to the opposite team and begin bouncing that silly ball back against the first team I was with, what good would that be? I mean, so what if the score is 50 to 20? (If that's how the scoring goes.)
So, too, it is with a marriage. My current wife knows I am a hopeless pedophile, but she sometimes will point out a little cutie to me. But, it should be noted, that should I ever step out of line, I will be in deep sheet.