We understand that you're struggling with intrusive thoughts about your former manager, and it's causing you significant distress. First, let's address the spiritual aspect of this situation. It's important to remember that our battle is not against flesh and blood but against the spiritual forces of evil. As it says in Ephesians 6:12 WEB, "For our wrestling is not against flesh and blood, but against the principalities, against the powers, against the world's rulers of the darkness of this age, and against the spiritual forces of wickedness in the heavenly places."
We need to pray that any ungodly souls ties between you and your former manager be broken. But first, let's address something important. You did not mention the name of Jesus Christ, Jesus, or Christ or even an abbreviation such as IJN (In Jesus Name). Maybe it is just an oversight, but it is important to understand it is only by the name of Jesus that we have access to God. Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by Me. John 14:6 WEB.
Going back to the main issue, when someone continues to invade our thoughts, it can be a sign of an unhealthy soul tie. A soul tie is an emotional bond that can be positive or negative. In this case, it seems to be negative and obsessive.
Let's also remember that we are to take every thought captive to the obedience of Christ. As it says in 2 Corinthians 10:5 WEB, "Casting down imaginations and every high thing that is exalted against the knowledge of God, and bringing every thought into captivity to the obedience of Christ."
We need to pray for God's peace and protection over your mind. It's clear that this person is causing you emotional harm, and that's not God's will for you. As it says in 2 Timothy 1:7 WEB, "For God didn't give us a spirit of fear, but of power, love, and self-control."
Let's pray together:
"Father, in the name of Jesus Christ, we come before You today to lift up our sister/brother who is being tormented by intrusive thoughts of their former manager. We rebuke these thoughts in the name of Jesus. We also ask for any ungodly soul ties to be broken right now. Lord, we pray for Your peace and protection over their mind. We ask that You would fill their mind with Your thoughts, Your truth, and Your wisdom. We pray that You would give them the strength to resist these intrusive thoughts and to focus on what is pure and lovely. We pray that You would give them clear boundaries and put a guard on their minds, Lord. In the end, we know God, that through your power there will be success in all aspects of this situation. Thank You, Lord, for Your promise to never leave us. In Jesus' name, we pray. Amen."
Prayer Focus: God, Thank You for loving me. Thank You for loving me, Jesus. God, I ask You in Jesus’ name bless me with everything that I stand in need of and everything You want me to have. Bless me to know You in truth, fall in love with You with all my heart, soul, mind, and strength and never fall out of love with You. Bless me to have an ever growing closer stronger, more intimate relationship with You. Bless me with the love, desire, strength, and the spirit of obedience to always delight myself in You, seek first Your kingdom, and Your righteousness. Help and strengthen me God to always respect and obey You. Bless me to trust You with all my heart, acknowledge You in all my ways, and lean not to my own understanding. 
