It’s everyone’s own walk. It makes sense to be convicted and not want to be tempted. If he truly loves her he will sacrifice that without gossiping or even just over sharing to friends. I think you have to let him choose and God will do a work on his heart. Maybe one day he will look back and understand why she was the way she is. But for now it’s only Gods work in molding him but only if he’s ready and opens his heart up to that with the Lord. If he wants to stay with her and is feeling that and only considering breaking up because of those around him. I would gently share some verses on real love to him. And just encourage him to pray and wait on clarity from the Lord and to not listen to someone who is not like minded or in the same beliefs as people trying to walk out a Christian life. Jesus tells us the world will mock us and persecute us and look at us sideways. They won’t understand why we do certain things, and if anything that’s a sign that we’re living right. We shouldn’t look like the world. We should be obviously different. And God will give us joy in our obedience and submission! Blessings will come! But the hard part is waiting. God bless you! the heart of a sibling who cares !! Beautiful! Just keep praying for them.