Both dramas have a minor/adult relationship that is very uncomfortable to watch.
Love and fortune is much less twisted but more difficult to watch because of the numerous graphic sex scenes (yes, between an adult a teenager) and because it is a longer drama.

In both dramas, jealousy and envy are main themes and the leads are long time female friends with an ambiguous relationship.
Kenja no Ai is much darker and more twisted.

Both dramas have a main couple with a 20+ years old age gap and a professionally successful female lead. Both dramas have the theme of sexual attraction and are depressing and angsty.