I’m really sorry that this happened to you and I find it hard to express in words on a mere net page my understanding of how this must really hurt. Whatever the reason, breaking up of a serious relationship hurts, and when it is the other person who made the decision, it is normal to feel confused, used, and perhaps a sense of lack of control.
I remember when I had a similar experience, I came to the conclusion that humans, even Christian brothers who do want to try their best to love and care for us, are still selfish and affected by sin. Relying on human relationships to give us satisfaction in life will ultimately only disappoint.
In these times it is useful to reflect on God’s faithful love. Reading Psalm 139 really helped me. The word of God comforted me by teaching me that God knows me inside out (Psalms 139:1-4), that He is never far away from me, even in my deepest depression he is with me (Psalms 139:7-12). Even though he knows how completely unattractive I am on the inside, He still loves me.
In the book of Romans, God also taught me that it is He who decides what happens to me in my life, and what He has given me is always for my good, and He does it because He loves me, even though at the time it doesn’t seem right to me (Romans 8:28).
Without knowing the details, it is hard for me to comment on how your boyfriend knows that it is God’s will for him to break up. In the Bible there are some clear guidelines to Christians as to whom they should not marry, for example, a Christian should not get married to non-believers, or someone they are related to, someone of the same sex, or someone who is already married. If these situations do not apply to your relationship, then there is no definite guidance in the Bible to say whether one person should marry someone or not.
(If you are not a Christian and do not understand why a Christian should not get married to a non-Christian, it would be really good to find someone other than your boyfriend who is a Christian who you feel you can talk to, and find out more about this, or you can feel free to ask another question here)
When there is no definite guidance in the Bible on something in life, it really comes down to each individual’s decision according to the wisdom that God has given the person. You may never be able to totally comprehend the reason for the break up in your boyfriend’s mind, but it is important for you to be assured of God’s love for you and that what He has given you is the best thing, even though it hurts.
Continuing to trust God, to believe in His goodness towards me, being comforted by reading the Bible and praying to Him, was what got me through the difficult times when I was let down by my Christian brothers and sisters over the years. I hope that you can find comfort in the same, and through this difficult period of time, may you grow in the knowledge and love of our God who loves you more than anyone ever could by giving you Jesus to die for you so that you can become His precious child.