Your obedience in stepping away from a relationship that was unequally yoked is heard before the Lord, and it is not lightly esteemed by Him. To walk away from what the heart has clung to, because you desire to walk with Christ, is a costly obedience, and it leaves a wound. That you now find the wound torn open by intrusive and jealous thoughts, thoughts that come unbidden and torment you with images of him with others, is a great ill, a brokenness of heart which only the Lord Himself can heal.
Scripture tells us, For My thoughts are not your thoughts, neither are your ways My ways, says the Lord. For as the heavens are higher than the earth, so are My ways higher than your ways, and My thoughts than your thoughts. Your thoughts in this season run toward loss and fear and a jealousy which is cruel as the grave, for whenever love has absorbed the heart, jealousy will guard its object and will not let go without pain. But God's thoughts toward you are not as your thoughts. His thoughts are constant, kind, wise, tender, gracious and perfect. How precious also are His thoughts unto us, how great is the sum of them. They are rare thoughts, higher and holier than our restless imaginings, and they are meant to become precious to us as we think upon them.
There is a great mercy set against this great ill, He healeth the broken in heart, and bindeth up their wounds. The Lord does not merely point out the disease, He applies the remedy. Calvary is the place of healing, and even the least thing about Christ has healing virtue in it, as the leaves of the tree of life are for the healing of the nations. Low thoughts of God keep the soul in bondage, but high thoughts of God beget hope, and hope brings confidence in His pardoning and healing hand. He who perceives our thoughts, for Jesus perceived the thoughts of those about Him, knows these intrusive thoughts that assail you, whether they arise from grief, from habit of mind, or from the assault of the enemy in spiritual warfare, and He is able to heal.
Do not be dismayed that the battle is in the mind, for the power of thought is that in which we bear something of the image of God, and therefore the enemy contends for it. You cannot have fellowship with God while your thoughts run contrary to His, but your thoughts can be conformed to His thoughts by faith. This is the work to which you are now called, not to fight these thoughts in your own strength, but to bring every thought into captivity to the obedience of Christ, to fill the mind with God's own thoughts until there is no room for the intruder.
When such a thought comes, turn at once to the precious thoughts of God. Say with David, When I awake, I am still with Thee. Let the first waking thought and the last sleeping thought be of your nearness to God through Jesus Christ, in whom alone is salvation. Store the Word in your heart, for faith comes by hearing, and hearing by the Word of God, and the healing power of Christ is present when He is teaching us by that Word. Put away whatever would suggest evil thoughts, and set before your eyes those things which lead the mind aright. Pray in that moment, sing a psalm, speak Scripture aloud, seek the fellowship of the saints who can pray with you, and ask the Lord to guard your heart.
We pray for you now, that the Lord who heals the brokenhearted would bind up your wounds and make your nature fresh again by His healing leaves. Father, we ask in the name of Jesus Christ, through whom alone we have forgiveness and access to Thee, that Thou wouldst grant our sister a quiet mind stayed upon Thee. Take these intrusive, tormenting thoughts away, rebuke the adversary who would harass her, and let Thy precious thoughts be her continual meditation. Heal the sorrow of this parting, turn this jealous pain into holy trust in Thy higher ways, and keep her pure and steadfast, reserving love and the gift of marriage, that lifelong covenant of one man and one woman, for its proper place within Thy will. If it be Thy will, bring to her in Thy time a husband who loves Thee, and until then, let her know that to be still with Thee is enough. Let her awake each morning and find herself still with Thee, till the joy of Thy presence makes her forget to say, I am sick, for Thou hast forgiven and Thou hast healed. Amen.