Co-Worker vs Friend

Disclaimer; I am extremely reserved and often hesitant about who I will call "friend".

A co-worker's birthday is coming up and it falls on a weekday. Another co-worker suggested we take her out for drinks after work. I said that I'd be willing to come, provided that he check with her first and make sure she doesn't have other plans. Seemed like common sense to me...why just assume someone you work with would rather hang out with you than a close friend, relative, or even her boyfriend? He seemed confused by this notion.

Temp: "Why wouldn't she want to hang out with us?"
Me: "She might have plans with friends"
Temp: "But we are her friends"
Me: "No...we are her co-workers"
Temp: "So you don't consider me a friend?"

My immediate response? NO! I have known you 3 months! The only time even we hang out outside the workplace is grabbing lunch or drinks after work, you know very little about me personally. How the heck is that a friend? If I said my dog died, he'd be remorseful right? Maybe buy me a card? A friend would say "Fool, you don't even have a dog!" Because my friends know ME... they know my likes, dislikes, strong points, and short comings.

But it felt wrong saying that. So instead, I responded by giving him a scenario. He said "but I know very little about her personal life". To which I responded "yet you call yourself her friend?"

A co-worker can be someone who you vent your work-related stress with. Someone you have lunch and maybe dinner with. A co-worker does not necessarily make a friend. I have been in workplaces where we were all a tight knit group but once someone moves on, the dynamic of the relationship is different. Are you now willing to make a sound effort to spend time with this person?

Until that is a mutual desire, you are...WE are..not friends.

Now the irony in the story; He double checked with her and she agreed to go out the day following her birthday for celebration! Que sera sera