"This is my boyfriend!"
Translation:Це мій хлопець!
Кавалер is not really the same as "хлопець". I think that кавалер is more of a date, someone who accompanies you to some event. And кавалер is kinda old-fashioned
"Коханий" - it can be both a noun and an adjective. In both cases it is used to refer to someone you love, as it comes from a word "кохання" (love)