What do you think happens next in the story?
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Leo is very disappointed but after some weeks, he will to be love for Anna .
Leo will be very disappointed in a few weeks, as he loves Anna.
Leo is very disappointed now, but in some weeks he will fall in love with Anna.
Do you want to say this?
in some weeks - (dans quelques semaines?)
fall in love (with) - tombre en amour (avec)
I don't know the story you are referring to, but my suggestions are...
Leo is very disappointed but in a few after some week's time, he will to  be in love with for Anna .
 Never "to" after the modal auxiliary verbs (can/could, shall/should, will/would, may/might, must) or after "do/does/did" from the verb "to do". Always the infinitive minus the "to" of the infinitive after these.