Not going to church is not a sin.
As a matter of fact, Yeshua never said anything about going to church....
And yes lusting for a woman is a sin.
You can make the aurgument that it's not a sin if you are not married.
But if that's the case, through out the scriptures YHWH instructs you to get married when you start feeling lonely. He'd rather see the fire in you contained under marriage then out of control with lust.
The commandments tell us that it's a sin to sleep with your neighbor's wife,
Yeshua inforced this by suggesting that the mere thought of it is a sin.
It makes sense when you think it about because He's talking about it at its core.
If my girl was having sex with some cat from her job, in her mind.
I'd be just as offended by it as if she had done it in real life.
What is the difference? She didn't actually do it, but the motive was there....