The burden you have poured out is felt, and it is right that you have brought it into the light rather than nursing it alone in the dark. Your desire for marriage is not in itself evil, for marriage is ordained of God and is honourable, but the trial you now endure is that of waiting, and waiting is a holy art which the Lord Himself must teach us.
You write that your father delays what you long for, that you have saved diligently, that your heart is strained toward your friends who are already married, and that you are tempted to think God has mocked you by giving a desire and then withholding its fulfillment, or by appointing for you one far below your hope. Hear this, that God does not tantalize His children. He is a waiting God who waits to be gracious, as it is written, Blessed are all they that wait for him. He often keeps us waiting not to punish us but to prove us, to wean us from self will, and to make the mercy sweeter when it comes in His own time. To run before the Lord is to wound your own feet.
You must labour to keep a right spirit toward your father. The command still stands, Honour thy father. Though you are near to mid twenties and provident in saving, which is commendable, you are not freed from reverence and meekness toward him. A bitter spirit toward a father will canker your own soul and will not hasten any good thing. Go to him not with contention but with quiet respect, open your heart plainly, ask his reasons, hear him as a son should, and seek the counsel of some godly older man in your church who may speak with you both. God often uses such mediation to soften hearts and to bring counsel to pass.
Despair is a grievous sin against the mercy of God, and you must denounce it as such. To say, let me take my life, or to wish for a heart attack that God might do what you dare not do, is to trample upon the blood of Christ which was shed to give you life, and to refuse the cordials which the Holy Spirit presents in the promises. Self destruction is not the will of God, nor is it escape. It is a leap into perdition, for our life is not our own to take, but the Lord's to give and to keep. Our heavenly Father has not brought you thus far to cast you away. If you trust your soul with Christ and with Christ alone, you cannot be cast away though your thoughts now tear you as the evil spirit tore the child while he was yet coming to Jesus. Go with this very temptation to the Mercy Seat and say, Father, are You there, will You keep me in this hour. He will with the temptation make a way of escape.
You ask concerning predestination and free will, and what purpose life has if all is fixed. Know this, that God is sovereign and man is responsible, and neither truth destroys the other. Your life is not purposeless while you wait. Your purpose today is to love the Lord your God with all your heart and to love your neighbour as yourself, for this is the law which God writes upon the new heart. It is not a law of mere outward restraint but of love. To live is to know Christ, to be conformed to Him, to serve Him in your daily work with all your might. You say you cannot focus on your work for tension and high blood pressure. That very work is the field where God would have you be faithful now. Do the right thing that lies before you and leave the result with God. Cast your anxiety upon Him, for He cares for you. If your body is pressed with high pressure and sleepless care, seek needful help and do not despise the means God provides, but above all learn to trust and not be afraid. Fear looks ahead and says, what shall I do when the rider on the pale horse comes, but faith looks to Christ and says, I will trust and not be afraid.
You say you are ready to marry out of the faith if only you may marry. I must speak plainly and in love, do not do this. The Scripture forbids the believer to be unequally yoked with an unbeliever, and marriage is a covenant before God of one man and one woman for life, to be entered only in the Lord. To break that rule to satisfy present longing is to sow sorrow for a lifetime and to set your soul in peril. The Lord who gave you the desire for marriage can provide a godly partner in His time, but He will never bless a path that turns away from Christ, who is the only way of salvation. Do not ask God to bless what His Word calls disobedience. Ask Him rather to keep you pure, to guard your heart from lust and haste, and to give you contentment in Him while you wait.
Seeing friends married while you remain single is a sharp trial, but comparison is a snare. Their path is not your measure. Your times are in His hand who made His own people to go forth like sheep, leading them by the right way though they knew it not. What seems delay to you is not forgetfulness in Him.
Therefore, take this counsel. First, flee to Christ anew and see that your soul is safe in Him, for without Him no marriage will satisfy. Second, bring your case daily to God in prayer, not in complaint but in trust, and believe that He hears. Third, seek peace with your father and godly counsel in your church. Fourth, keep your hands diligent in your work and your body in temperance, refusing to feed despair with idleness or impure thoughts. Fifth, put far from you every thought of self harm and speak at once to a faithful pastor or brother if those thoughts press again, that you may not be alone in the conflict.
May the Lord who writes His law of love upon the heart write patience there also, and keep you from the sin of despair, and in His good time provide for you as seems best to His infinite wisdom.
Prayer Focus: God, Thank You for loving me. Thank You for loving me, Jesus. God, I ask You in Jesus’ name please bless me with everything that I stand in need of and everything You want me to have. God bless me to prosper, walk in excellent health, and never stop growing in the love, grace, wisdom, and knowledge of Christ Jesus. God bless me to know You in truth, fall in love with You with all my heart, mind, soul, body, and strength and never fall out of love with You. God, 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, Your righteousness, and to always respect and obey You. Bless me to know You, the way You want me to know You. So that I will trust You with my life and anyway that You move in my life. Bless me to trust You with all my heart, lean not to my own understanding, acknowledge You in all my ways, and allow You to direct my footsteps and actions. Bless me with knowledge, wisdom, and understanding in all You have called me to do. 
