Chinese manhwa

Actress accidentally enters portal to ancient times, brings back guy

Prince pretends to be dumb and bad at everything to avoid fight for the crown. His wife cheated on him with his brother.

Fl is ugly girl from modern times, gets plastic surgery and looks identical to prince wife. Gets thrown into princes timeline and replaces princes wife. Prince fights for crown to protect fl.

Fl falls for ml and goes with him in 3 lifetimes to help him pass test for immortality. She is his sister in 1st life and classmate in 2nd, and master in 3rd. They have kids together end of story.

Mermaids hide away from dragons because dragons stood something from mermaids long ago. Dragon needs to steal something again so ml looks for FL to trick her.