[ Proverbs 4:23 - Keep your heart with all vigilance, for from it flow the springs of life. ]
This is something I failed at a lot in life and had to learn this the hard way. God tells us to guard our hearts and who we let into the closest intimate parts of who we are because of its immense worth and also the fact that it will determine the very course of our life. Sadly, not everyone out there has the best and pure intentions for you. Many have learned the evil power of manipulation that once you have someones heart in your grasp you can turn it to your will whenever you want and get people to do just about anything. The solution to this isn't building high walls to keep people out, becoming cold, distant and suspecting of everyone. Instead, the solution is to have a source of wisdom that knows the heart of others even before they speak or act towards you.
That source of wisdom is called The Spirit of God. He is our comforter, our guide but also that voice of warning when danger is present to guard you from unnecessary harm. He protected many in the Bible and He's still very much doing it today. He speaks, guides, teaches and warns because of His immense love for us. His voice is quiet, calm, clear, deliberate and it always speaks in absolute authority. Everything He says is a direct echo from the heart of your Father in Heaven. Pray and ask God to develop your spiritual ears to better understand, hear and obey the voice of the Holy Spirit and He will lead you in the paths that God has for you.
David said it perfectly when He penned Psalm 143:10 "Teach me to do your will, for you are my God! Let your good Spirit lead me on level ground!"