You flirt with guy at work and he flirts back. You ask him to let you teach him tennis. That's basically a date at this point.

If I was your BF, and I heard this story, I would nod and smile and plan my exit because it sounds like you and your work friend are probably fucking already.

If you come home one day and he's gone, that's why.

Stop flirting with and planning dates with other dudes if you respect your BF.