Everyone has boundaries, whether they refer to them as boundaries or not. A lot of Christians set certain boundaries in their dating relationships (saving first kiss for marriage, having chaperones at all times, etc.). These boundaries help us to keep our physical and emotional purity. However, if our heart is dwelling on things that go beyond these boundaries, we will slip up.
If our hearts are not in it, and we’re following the rules but dwelling on the things beyond these rules, that creates a perfect breeding ground for sin.
The Devil will see your weakness and try you harder than ever.
The Lord sees what is going on in your heart. Even if there isn’t a soul on earth that knows what you’re thinking and feeling, God does. He also judges you by what’s in your heart (Hebrews 4:12, Genesis 6:5).
God wants your heart to be right before Him.
He doesn’t want you to go beyond the boundaries you have set, if they jeopardize your purity and relationship with Him. But, if your heart isn’t in the place it should be, the temptation to sin is so much greater than if your heart desired the will of God in your life.
But, God isn’t going to let you do it alone. If you are struggling with thoughts and temptations in your heart, He wants to help you. Look at Psalm 26:2 and Psalm 51:10. If you want to be right with God, He will help you get there.