Thank you for sharing this so honestly, and I know this kind of pain is very hard to carry. Wanting to do what is right before the Lord while still caring deeply for someone creates a real ache, and it is right to bring that ache to God in prayer.
Your decision to step away because you were unequally yoked was a step of obedience to Scripture. The Word says to not be unequally yoked together with unbelievers, and asks what fellowship righteousness has with unrighteousness, what communion light has with darkness, what part a believer has with an unbeliever, and what agreement the temple of God has with idols. That principle is not limited to marriage, though marriage shows it most clearly. Any close binding where two lives are yoked together to pull in the same direction will be unequal if one follows Christ and the other does not. You will not be living by the same standard or the same ethic, and that unevenness always shows itself. Many people feel their situation is the exception and that love will be enough to cover the difference or that the other person will change, but Scripture gives this counsel for our protection because those two ways of life are like oil and water and do not truly mix. God calls His people to come out and be separate, and promises to receive us and be a Father to us as we walk that separated path. Your willingness to obey in this is not a mistake to regret, even when it hurts.
It is understandable that worry has come in now, especially with his health problems and the silence between you. When you have no way of knowing how he is doing, the mind can spin with questions about tomorrow and with second guessing, wondering if you said the right thing or made the wrong choice, and that kind of melancholy worrying can linger for weeks. But worry does not help solve anything and it has no real value. Jesus taught that worry cannot add anything to our lives, and that most of our worry is about tomorrow rather than today. Faith and worry move in opposite directions.
The answer Scripture gives to worry is prayer. Instead of being anxious, we are told to be anxious for nothing, but in everything by prayer and supplication with thanksgiving to let our requests be made known to God. Rather than carrying the burden of what you cannot control or know, you can commit this man and his health fully to the Lord. You can thank God that He sees and knows what you cannot see, that He knows what this man needs, and that His ways are higher than our ways. We cannot always understand why some face serious health struggles while others do not, and physical health is not a simple measure of spirituality. Some of the most faithful believers walk through great health difficulties, and that does not mean they lack faith. God is sovereign over life and health, and He is the one who cares for him now even when you cannot.
When you turn worry into prayer and trust the Lord to do what is right, He promises a peace that passes understanding to guard your heart and mind in Christ Jesus, even when circumstances remain painful and unresolved. People around you may not understand how you can have peace in such a difficult situation, but that peace comes from leaving the matter in His hands.
I will pray for you, that God will steady your heart, confirm you in the right choice you made to obey His Word, and fill you with His peace as you trust Him with the future. And I will pray for your former boyfriend, that God would have mercy on him in his health needs, draw him to salvation through Jesus Christ alone, and work in his life according to His perfect will. The kindest way you can love him now is to place him in the hands of the Father who loves him and knows exactly what he needs.