Name: Natasha | Who: your best friend. (Informal)
... this is Natasha, she's my best friend. / ... meet Natasha, she's my best friend.
Name: Bobby | Who: your сolleague. (Formal)
Mr. ... I'd like to introduce you to Bobby. He's my colleague. / Mr. ... I'd like you to meet Bobby. He's my colleague.
Name: Franco | Who: your boyfriend. (Informal)
... this is Franco, he's my boyfriend. /... meet Franco, he's my boyfriend.