I'm so sorry to hear that you have lost your brother. That must have been so difficult for you and your entire family. As a mother, I can't imagine how difficult it would be to endure losing a child.
In regards to getting married and having kids, it is hands down, the most important decision you will ever make. When you have kids, you are literally promising to care for, guide, counsel, correct and provide for another human being, and you are responsible for their well-being until they are 18 years old (legally), but I can tell you truthfully, it goes on much past the 18 years required by law. Once you become a parent, something shifts in regards to their well-being.... IF it doesn't, something is wrong, because it should. It's not something to enter into lightly, nor is it something to do in order to please someone else. It must be something you want, or you could potentially resent your own kids, and also your mother. Getting married and having children is not for everyone. Some people are better off staying single, and never having kids...or getting married, but never having kids. If you meet a man and the two of you fall in love, you will decide together if you want to have kids. It's a personal choice for that couple to make.
It's okay that you spoke in anger and said you will never marry anyone. You were likely having an emotional response during an extremely stressful time...that's totally normal. If you feel now that you are changing your mind, that's okay too. Please don't let anyone pressure you though... It's not anyone else's business. Pray for God to give you wisdom and direction in knowing this. Wisdom is needed here.
I will tell you this-- I am married with two boys. Before I met my husband, I never thought I would want kids. But then I changed my mind. They are both incredible young men. I'm so completely overwhelmed with how blessed I am and how wonderful it is to be a Mom.
Your heart is tender towards God and your promise, and that is a beautiful thing.
It's important that we don't take God's Grace and Mercy lightly, I believe you take your promises before God very seriously, and that is the right thing to do... But, having said that, a few scriptures come to mind:
Psalm 103 14 For he knows how weak we are;
he remembers we are only dust.
Psalm 86 15 But you, O Lord,
are a God of compassion and mercy,
slow to get angry
and filled with unfailing love and faithfulness.
2 Samuel 24 14 “I’m in a desperate situation!” David replied to Gad. “But let us fall into the hands of the Lord, for his mercy is great. Do not let me fall into human hands.”
My point is, God is merciful. He knows we will sometimes make promises or say things that we can't keep. I suggest that you go to God and just be honest. Say something like "Father God, My Creator, Redeemer, Lord and King. I made a promise to never marry. I'm sad now because I feel differently about it. I think I might want to get married one day, and I should never have made that promise. Please forgive me. Thank you. I'm so grateful that you understand how weak I am, and you also understand why I made the promise in the first place. I'm asking Lord for your blessing to one day be married and have children of my own. Please confirm it to me that I have your blessing, as I can't imagine getting married outside of You blessing my relationship and my family. I ask this in Jesus' name...the Name above all Names. Amen"
God is interested in redemption and blessing. I've heard people say that God is a God of second chances.... But He is so much more than that. He is The God of more chances.... it doesn't stop at second chances. Simply confess your sin to Him.
1 John 1 9 "But if we confess our sins to him, he is faithful and just to forgive us our sins and to cleanse us from all wickedness."
1King 8 23 "He said, “O Lord, the God of Israel, there is no God like You in heaven above or on earth beneath, keeping covenant and showing lovingkindness to Your servants who walk before You with all their heart..."
Proverbs 3 " 5Trust in the Lord with all your heart
And do not lean on your own understanding.
6 In all your ways acknowledge Him,
And He will make your paths straight."