"Then, after desire has conceived, it gives birth to sin; and sin, when it is full-grown, gives birth to death."
Being a Mom, I resonate with the word picture of this verse. Having gone through the process of "thinking about conception" and then conception itself...the growth process leading to birth, and realizing that we all face the ultimate end: death. There is a vivid message here.
Affairs don't happen because a spouse (husband -OR- wife) looked at someone else and thought they looked cute. No, it happens when someone looks, lingers, thinks and contemplates how that person looked (or treated them so nicely, or seems so Godly a spouse, or was so much neater than..., etc, etc, etc). Over time the thoughts begin to settle in and become comfortable, and before you know it the sin has become full-blown and there's nothing ahead, it seems, but a slippery slope.
There are two things to remember, then:
1) Guard your heart, for out of it flows the well-spring of life. Don't let those thoughts take root ~ surrender the desire and the feeling to Christ. A companion to this is that God does not tempt us...but He does give us the strength (HIS strength) to walk away when we simply say, "HELP!"
2)There is no sin so great God can't redeem it. Confess and repent to God your sin. Then take hold of James 1:9 that says we can ask for wisdom when we don't know what to do...then look for His leading in what to do from there.
Sidenote: I am not so naive to think that sin always looks ugly. Sometimes we've become so comfortable with it that we really don't want to stop thinking about it or doing it. It is in those times that you can ask God to make it ugly to you....ask HIM, the One who created you, to change your mind about it. He is faithful, and He will, in the words of an acquaintance, "catch your conscience." If you still don't want to...see it through to the end in your mind's eye. Sin is never worth the end result.