"Two men went up into the temple to pray, one a Pharisee and the other a tax collector. The Pharisee, standing by himself prayed thus: 'God I thanks you that I'm not like other men, extortioners, unjust, adulterers, or even like this tax collector. I fast twice a week; I give tithes of all that I get.' But the tax collector, standing far off, would not even lift his eyes to heaven, but he beat his breast saying,'God, be merciful to me, a sinner!' -- Luke 16:9-14
I must be completely honest here. Every time after I fall into sin, a great overwhelming feeling of grief and brokeness cover me. Why? Cause I have sinned against the One True God, the creator of the universe, my Father! Just the thought of what I've done, whether it was a little lie or having lustful thoughts towards a woman, or using His name flippantly, or whatever will make me put my head in my hands, to my knees, weeping, begging God to forgive me for doing such a wretched thing.
When you weep over your sin that sure sign that you are truly in the faith, that you are a true Christian. Though if you recognizably sin, yet dismiss it saying to yourself "Oh I need to make sure I don't do that again", or something like that then I suggest you read through 1 John to test yourself and see that your in the faith. If you truly are saved then you will hate sin to the point that whenever you fall into sin, you are broken and grieve over it.
"Blessed are those who mourn, for they shall be comforted."-- Matthew 5:4