Afraid of losing his cushy corporate job, a slacker concocts a story about a fake ex-fiancé who left him at the altar but when he falls for a girl with the same name, he must keep her a secret to keep his job.

Can't he just say "I met a girl with the same name"?

Maybe he can fake a depression (caused by?the said?being left on the altar), so he will need to hide the joy of his couple or being fired.

The structure make me think about the movie "Le Placard" de?Francis Veber, where the main character learns that he's about to be fired, but a friend tells him that he won't be fired if he's gay because the company needs to avoid criticism about being homophobic (they sells condoms).
So he must?do his "coming out" (but he's not gay!) and he falls in love with a female collegue so he needs to hide it. Wow, this was truly a good concept for a comedy.

Agreed with DPG, also what is at stake? His job?
Albeit this is a comedy, but still it needs a compelling plot or in other words; it needs higher stakes than a job.

Why does he have to concoct a lie about being left at the altar to keep his job? ?I don't understand the cause and effect relationship between the two.