What should I do about my husband, who loves another woman online after ten years of marriage, and will this relationship end?

Forbidden romantic relationships, whether online, over the phone, or by other means, are a clear abomination and prohibited. If they escalate to dating, meeting, and committing indecency, then this is utter destruction. It is a stupor, heedlessness, and a veil from Allah, as the Most High said: "By your life, indeed, they were aimlessly wandering in their intoxication." (Quran 15:72). One must praise Allah for good health and purity, and be patient with this affliction, which expiates sins and elevates ranks. It is appropriate to supplicate for the afflicted woman, asking Allah to rectify her condition, and to increase supplications during times when prayers are answered, and to try to win over the husband's heart with gentleness and adornment. Allah gives respite to the oppressor until, when He seizes him, He does not let him go.