You may very well not know what kind of correspondence you are receiving from this person, but not all of it is aimed at polite society.

the reason you don't understand the "tres fort" part is that this would be transliterated from French to English as:

I have desire for you -- very strong

colleagues -- Je pense que notre cher asker joue avec nos pieds eh! Il sait bien que ce phrase parle des rapports sexuelles -- mais il ne pige rien de 'tres fort'? Je ne le crois point!

Sous réserve quand même d'une distincte impressions que, comme chez la personne qui a fourni la réponse précédente, on se fiche de nous un peu ici?

I too agree with the previous answerer that it refers to a sexual desire and not just a banal "I want you...". "J'ai envie de toi" is always used, in French films at least, when some guy is explaining to a girl just how much he want to make love to her. The fact that the sentence places the "très fort" further away in the extract only serves to emphasise this.