One of the mistakes that I often see people make when hiring is mistaking popularity and personality. This leads to disaster after people have been on your team for a while. Someone who may have seemed like a great hire ends up causing all kinds of problems with the rest of your team. Or vice verse, is never able to become a part of it and ends up leaving. Unfortunately, the reality of hiring, especially in the tech sector and start-up world, is that a lot of people who may be great colleagues aren't necessarily people you'd be friends with. Again, this works in both directions. They probably don't want to hang out with you after work neither and that's fine.
No one ever said that the people you work with have to be the folks you socialize with outside of work. In this touchy-feely, politically correct day and age it's often forgotten why we go to work. Love it or hate it, you go to the office first and foremost to get stuff done. We can debate endlessly about whether you should love your job or not but no one will argue that it exists for you to do things.
Thinking you can always work with the best and always be friends too is delusional and striving for that with each hire is nuts. I'll admit that some of the best people I've ever worked with were total freaks. Sure I'd go grab a beer with them after work here and there but I wasn't planning family vacations with them nor spending weekends out with them. They too were not necessarily inclined to spend a lot of free time with me. Even more amusing is that I'm best of friends with some people whom I worked with. I hated their guts though when they were colleagues and couldn't stand them in a work environment.
It's not rocket science but bears repeating. Just like trying to be your kids best friend will cause problems, so too will trying to be best friends with your colleagues. It's great if colleagues click on personal level and spend all their waking hours together. Just don't bet on it nor expect it. People have their own personalities and may not click with you privately. This doesn't mean they shouldn't be your next best hire.