Very good, Andrey!

Elena and Grumbler, although your versions aren't incorrect, the word ALREADY is kind of superfluous. The perfect tense gives the sentence a sense of ALREADY, so it isn't necessary in a sentence that describes a process. If you DO decide to use it, it should ideally go after HAVE: They've already been going out for 3 years.

USE CONTRACTIONS!!! They make your English look more natural :)

All right, thank you, Uly, for your corrections:)

Always a pleasure, Elena :)

Uly, I appreciate your comments!

Good job, Andrey :) Your translation is the most idiomatic.