君がいなくて寂しいよ。

you; buddy; pal; monarch; ruler; sovereign; (one's) master

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

indicates certainty, emphasis, contempt, request, etc.; used when calling out to someone; used to catch one's breath or get someone's attention; yo!