I don't own The Crazy Ones and never will. No copyright infringement intended.
It happened because Simon and Zach got a little too excited about the ideas for their latest pitch. Neither expected it, but both of them found out they didn't mind too much. After Simon launched into his latest rant, Zach kissed him to shut the older man up. It worked. "Wow."
Zach laughed. "Yeah." Now it was a little awkward, but he didn't regret doing it.
Simon shrugged. "You want to do it again?" He wasn't bothered at all because he was bisexual and had had several relationships with men over the years (in fact, he and Lewis had kissed once, but found they were better off as business partners).
Zach didn't even have to think of it. "Sure, why not?" It wasn't like he hadn't thought of this happening before.
Simon went in for a kiss again and the two of them were making out within minutes. Lauren came in at one point to close the blinds (but lingered for a few seconds before Sydney pulled her out) so they could have some privacy.
Much to their surprise, Simon and Zach's relationship continued and it actually worked. The fact that they were happy with each other helped a lot.