You are asking me a good question, one that I wanted to take the time to put together a thoughtful, written response to address. Please keep in mind that I am neither seminary educated nor am I a licensed professional counselor. You might well have paid either of those people for their advice, and my advice is free. My advice might be worth what you paid for it, but I will do my best.
This is a very important decision. Many would call it the single most important decision you will make outside of the decision to follow Christ. I would like for you to be careful because of this decision’s importance, but not too careful. Your spiritual life is simply not ultimately dependent on this decision; the small decisions you make every day concerning whether to believe the gospel and be obedient to God’s Law are simply more important.
I don’t want you to mess this one up, but many Christians with strong faith have, and they will join us all in heaven. Romans 8:28 applies here. Concentrate on loving the Lord. He has called you according to His purpose if you have placed your faith in Christ, and this verse applies to you. All things are going to work together for your good to conform you to Christ’s image, not just some things. I know you to be an ardent perfectionist, and I want to guard you against being entirely too particular. I don’t want you to be impulsive, either; but many, many young people have passed up perfectly good marriage partners because of a desire to find the person exactly suited for them. Some have lived to regret their decision as life unfolds.
Please don’t put out golden fleeces, expect to hear the literal voice of God in prayer, or expect strange or intense feelings to be a reliable guide to the leading of the Holy Spirit. Many have been led astray by mild indigestion they have experienced because of the pizza they had recently eaten. To hear God’s voice, read the entire Bible. Then apply your intellect. Use your head! And for heaven’s sakes do not become physically involved with anyone outside marriage. That will result in strange and intense feelings that are extremely difficult to resist.
Where exactly would I go in the Bible? First, don’t marry an unbeliever; or, by implication, a scoundrel (2 Corinthians 6:14). Be discerning and get the advice of others close to you who may not be infatuated. That, of course, means spending time with each other’s family and friends. That is always a good thing, and it also helps you to see whether they interact with others in a godly way. You don’t want someone prone to unedifying speech (speech that tears down others) or gossip. You will be listening to her speech for a long time.
Where else would I turn? The entire book of Proverbs. Yes, that’s right, read the whole thing. It has thirty-one chapters, so one chapter a day is a good pace. Hopefully, it is not your first time to read the book, but if it is, you don’t have to tell anyone. Remember, these are ‘rules of thumb,’ and not necessarily moral absolutes. Consult a conservative study Bible such as the ESV Study Bible and read the introduction to get at my meaning here.
Now that we have dispensed with the Experiencing God approach to discerning God’s will, I will move on to some more pointed advice. Find someone who will help you follow the Ten Commandments. Remember that “The moral law is summarily comprehended in the ten commandments” (Westminster Shorter Catechism Q and A 41). You want someone to help you live according to God’s Law. It’s that simple.
Also, they need to help you better understand and reflect on The Gospel (For a definition of the Gospel, see links here and here). Make sure she can clearly articulate what God has done for us in The Person of Jesus Christ. She may not use erudite theological language, and that’s OK. But you can’t teach what you don’t understand, and you want someone who can teach you the gospel. We all need to be reminded of God’s grace in Christ when we screw up. Not if we screw up, but when! She needs to have acted on the gospel beyond just understanding it and repented of her sins and placed her faith in Christ, but we covered that one above when we said she needs to be a Christian. And make double sure that she has the same understanding of the gospel you do (All of God’s grace, not any of our works at all whatsoever.).
I’d like to remind you again that this doesn’t have to be a perfect decision. In fact, it won’t be! There are no perfect people, Christ excepted, and to expect otherwise would be extremely foolish. Even if you make a bad decision, God’s providence will ensure that it works for your good and will conform you to Christ’s image (See Westminster Shorter Catechism Q and A 9-11.). For the believer, God’s gracious providence is the ultimate ‘safety net.’ I say this as a person who has had his heart broken and who has broken others’ hearts (I have both an ex-finance and an ex-wife out there, remember.).
I wish you well in your endeavor. You have already demonstrated your sincerity and determination by getting an excellent education and becoming the kind of person who women would desire to marry. That is terribly important.
Lastly, do not allow yourself to be snared by the devil or entangled by the world, even if you never find a partner. Many spiritual giants have remained single their entire lives, and you should be willing to do so if that is what God requires of you.
God bless you, and I pray He provides His good and gracious providence on your journey.