Can someone who unjustly divorced, repented, but whose ex has remarried, now marry someone else? Yes — the previous marriage is clearly over both legally and morally once the ex has remarried. The wrongly-divorcing party has repented. The alternatives (permanent singleness as unforgivable punishment, or pretending the marriage still exists) don't make biblical sense.

Two untenable alternatives: (1) treating it as an unforgivable sin requiring permanent singleness, (2) claiming the original marriage still exists despite the ex's remarriage. Neither fits Scripture. The repentant party is free to remarry but should do serious soul-searching, pastoral counseling, and address the heart issues that contributed to the original failure.