How do you say in french I yearn for you?

There are several ways to say "I yearn for you" in French, depending on the level of formality and intensity you want to convey:

Formal:

* Je vous désire ardemment. (I desire you ardently)

* Je vous aspire avec ferveur. (I aspire to you with fervor)

Informal:

* Je t'aime beaucoup et je te manque. (I love you very much and I miss you)

* Je rêve de toi. (I dream of you)

* J'ai envie de toi. (I crave you)

* J'ai hâte de te revoir. (I can't wait to see you again)

Poetic:

* Je suis en proie à un désir ardent pour toi. (I am prey to an ardent desire for you)

* Mon cœur se languit de toi. (My heart longs for you)

The best translation will depend on the specific context and the relationship between the speaker and the listener.