Spend some time learning about the concept of the excluded middle[1]. It is something that will be useful on your life going forward, it might even save you a lot of trouble.
I am writing a post about that for my blog but it's still not there so ... check back later? Lol.
Anyway, in this particular scenario, a co-worker not being my friend does not mean we are enemies.
> You can make friends on your free time.
Most well-adjusted people work to live, they don't live to work. Life comes first, the demands of the job come a distant second.