WHEN A SIN IS NOT A MISTAKE

I'm no philosopher.
I'll never make my own definitions of the complexities in life. That'll be too exhausting for my tiny brain. I've read in books the definitions of sin, and I discussed with a friend about his definition of it. Honestly, I am left much more confused than I was before the discussion.

A sin is doing something God forbids, and/or not doing something God orders you to do, according to The Poet.
A sin is something you do, and you're scared that somebody will find out about it, according to my highschool teacher.
A sin is violating an agreement with another party, according to a friend.
A sin always means making a mistake, but a mistake is not necessarily a sin, according to all three.

I'll just admit it, by any definition, what I do with you is a sin.
But until the last day of dear life, I'll never be able to admit that it is a mistake. Because to me, it simply isn't.

That's what I think of, dearest, when I first lay down next to you, holding your head against my pounding heart. A sin is a sin, but how could loving you be a mistake?

You see, that is how confused a tiny-brained woman can be.