What does a cross on the marriage line mean?

What this means

First confirm the mark is a true X on the small relationship line below the little finger, not a shadow, skin crease or separate child-line mark.

A deep clear cross carries more weight than a faint mark; weak marks should be read as light or temporary evidence.

Compare nearby breaks, forks, islands, the heart line and both hands before saying anything about separation or long-term commitment.