Loveless means without any affection in it. A loveless marriage, a loveless childhood, loveless and cold.
It almost always attaches to a relationship that ought to have love in it, which is what makes it sad rather than neutral — a loveless marriage is a marriage that has failed at its own purpose. It is stronger than unhappy because it names what is missing. Note that -less here means without, as it always does.
1adjectivelovelessWithout any affection in it.
“She grew up in a cold, loveless home where nobody ever hugged her.”
loveless is a quality of absent affection.
Middle English loveles is love plus -less, an Old English ending meaning without. Fruitless and hopeless are built the same way.
Middle English
loveles
English, today
loveless
From Middle English loveles; equivalent to love + less.
Etymology from Wiktionary, CC BY-SA