Your "colleagues" become your "work friends" and, eventually, simply your friends.
Particularly when you're working a full time gig and you start to spend more time at work than you do in your own home, it's important that you at least sort of like the people otherwise known as your "colleagues"; but, what's even better is when you start to sincerely enjoy their company.
Your work friends know things about your life that a significant portion of your own family does not.
It's safe to talk to them because they only ever see you in the office, so what harm could possibly be done?
You look forward to going into work.
Not necessarily because you love your job (although, congratulations if you do), but because you know that you can get the details on the fight Sally had with her roommate last night and that, in turn, she'll give you some advice on that significant other who's really just more of a complication than anything else.
When customers aren't around, you can be foolish around one another.
Whether it be writing notes back and forth; making faces at one another; or, simply laughing a little to hard at an anecdote… there is no judgement, especially after a long day.
Your work friends give truly solid advice without any judgement or bias because they don't actually know the people you're talking about.
You have circles. You have your work circle and our student circle and your friends circle and maybe even a few others, but the thing is: your "work circle" and your "friend circle" don't really overlap so venting about what went down last weekend to your coworker Brad is actually a pretty secure conversation (most of the time.)
Too many inside jokes to count.
No explanation necessary.
A large majority of your recommendations-Netflix binges, new restaurants, etc.- come from work.
When you spend all of your time in the office, it's not surprising that some of your tendencies at home will change because of the advice you have received there.
You all have a group chat (that tends to include a few drunk messages.)
GroupMe, WhatsApp, you know it.
You fight like siblings.
It's inevitable and clearly you'll get through it, but when you spend a significant amount of your time together it's nearly inevitable that you're going to argue sometimes. And, in a close-knit office, it's going to be the talk for a little bit. But you'll get through it, because work just gets plain awkward if you don't.
