Quote from elkpark
There are only a few times in my long career I've ended up maintaining friendships with "work friends" over time after leaving the job. "Work friends" aren't the same as "real" friends; it's helpful to understand the difference and not expect more from the relationship than it is.
On the topic of "work friends" in general, I have found this to be true. If the "friends" were people that I spent time with immediately after work, and all we talked about was work, then these are "work friends".
If we go on weekend trips together, our families know each other, etc. We are "real friends". If I have friends that I knew before my current job that you are now friends with also, I consider you a real friend.
I will never forget hanging out with someone and we ran into a few of her "real friends" at a restaurant and she introduced me by name, followed by, "we work together and had a long day". Although I took notice, I didn't really take it personally until I left job and experienced EXACTLY what you did, BlinkyPinky. So, don't take it personally, it is what it is!