Your prayer has been heard, and the heaviness you describe is real. Thank you for beginning with thanksgiving even in pain, and for wanting God's will above your own. That desire to say your will be done is the right anchor when the heart feels so torn.
It is understandable that this burden feels so heavy and unbearable, and that you cannot get this young woman off your mind. When affection grows strong it can take hold of all our thoughts and become like a tyrant that never rests, demanding more and more of our strength until we are consumed. That is why Scripture calls us to bring every affection under Christ and to let His grace and His Word heal and order our hearts. The precious blood of Christ, received with faith, and the steady hearing of Scripture, and turning outward in love to serve others, are the means God uses to quiet and mortify those passions that would otherwise devour us.
Part of loving as God loves is to love for God's sake and not only for our own comfort. True love does not press forward contrary to what seems good to God, and it does not force itself where it is not welcomed. You have said you tried to be her friend and she shows no interest, and that you let hurt and anger keep you from even looking at her. That honesty matters. To love her rightly now means to respect her no, to not pursue what she has not welcomed, and to refuse to let hurt or anger rule your actions. Even if you are only feet away, you can choose courtesy and kindness without demanding friendship or more, and you can also choose wise distance so that your heart can heal and she is not pressured.
You spoke of faith the size of a mountain to move God in this situation. Faith the size of a mustard seed is not a force to make God grant what we desire, but trust that God is good and wise and will do what is best. God in His longsuffering draws us to repentance and to trust, and He certainly hears prayer, but His answer is always according to His perfect will. The very fact that this burden is heavy does not in itself mean God intends you to be together. Sometimes a heavy burden is God's call to pray for another person's good and salvation, to learn to surrender, and to be shaped to love more purely. If God has not opened this door, His no or His waiting is also love, meant to protect both of you and to lead you into greater wholeness.
Any future relationship that honors God will be as Scripture teaches, salvation through Jesus Christ alone, and marriage as a lifelong covenant of one man and one woman, with love and physical intimacy kept within that covenant. That is the path where love can truly glorify God and do good to others. Until and unless God clearly leads two people together in that way with mutual consent and peace, the calling is to walk in purity, self control, and respect.
So bring this burden to the Lord daily, but in a new way. Ask not only if you might be together, but ask God to make you like Christ, to heal your heart, to help you forgive any hurt, to take away anger, and to teach you to love all people as brothers and sisters with a love that seeks their good. Pray for her too, for her faith and wellbeing, without making the prayer a way to hold on. Stay in the Scriptures, stay close to the fellowship of believers, serve the poor and needy around you, and let God fill the space that longing now occupies. If thoughts of her return, gently turn them into a brief prayer for God's will for both of you and then turn your mind to your duties before the Lord.
Let me pray for you.
Lord Jesus Christ, thank You for this brother and for his honest heart. You see his heartbreak and his burden. Have mercy on him and give him peace. Teach him to trust Your will above all, to respect this young woman and to do her no harm, to let go of anger and hurt, and to walk in purity and self control. Heal his heart, guard his mind, and fill him with love for You and for others. Draw him closer to Yourself, ground him in Your Word, and lead him by Your grace. And Lord, bless this young woman according to Your perfect knowledge and love, draw her to Yourself, and keep her in Your care. Let Your name be glorified in both lives, and grant to each the good things You have promised to those who love You. In Jesus name, amen.
Keep seeking the Lord first, trusting that whether He opens or closes this door, He will not waste your pain but will use it to make you more like Himself.