あなたがいなくて寂しくなるでしょう。

you (referring to someone of equal or lower status); dear (what a wife calls a husband)

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to be (of animate objects); to exist; to stay; (after the -te form of a verb) verb indicating continuing action or state (i.e. to be ..ing, to have been ..ing)

lonely; lonesome; solitary; desolate

to become; to get; to grow; to be; to reach; to attain; to result in; to prove to be; to consist of; to be composed of; to succeed; to be complete; to change into; to be exchanged for; to play a role; to be promoted; to do ...

death