two-day-boyfriend

Noun
The man you fuck, enjoy getting to know, engage in a fun activity with, get to know the best side of and let him see the best side of you, all without investing any feelings in each other as you both know that in just a few short days you will never see each other again.

Friend 1: "We had a great time and he was a great person. I really enjoyed my time with him."
Friend 2: "Do you miss him?"
Friend 1: "Nah, he was only a two-day-boyfriend"