I agree 100% that the burden of prove is on Gomer. She has to prove that she is now a faithful follower of Jesus. And that she has no intention of repeating her past. And she truly see you as special to her and she shows them clearly through her actions.
I believe 1 Corinthian 7:39 applies here to both ladies and gentlemen. Never mind just the Gomers. When we date anyone we must test their faith to make sure they are truly in the Lord. Do they pray to God a few times every day? Do they seek God's wisdom? Do they read the bible, listen to sermons, discuss in small groups outside of their Sunday church? Do they seek to help the poor, the homeless and anyone in need? Most important do we see them truly loving others because they love Jesus?
If the Holy Spirit is in them, we will see the love in them.
Every situation is different. If a man is dating a Gomer, he must pray ever harder for very clear signs from God.
If she is indeed changed for the better. And if he think God calls him to marry her. But her past is still holding him back, he should pray for more faith that he can truly forgive her.