Out of Touch, So Soon?

I remember my mom telling me that her closest friends that she has kept in close contact with to this day have been those she met in college, which makes perfect sense being that we're older. What I've been wondering is if this holds true to me, because even though I'm generally not a person to constantly keep in touch with anyone, my friends from back home who I've known since grade school and high school are the ones who's bond is the strongest.
In college, I met alot of people, very fast. There was the freshman dorm where you basically had 60 students living together. That was seriously the best times, when everything was brand new, and everyone was excited to make friends. When people moved on to their own housing plans after dormlife, I lost touch with many of them. How many times were the words "We need to hang out soon, I miss you" been told, with no action taking place. As if words now meant more than action....as long as they mentioned or thought about me, I guess we're still friends.
But what happens when college takes on the full effect? AKA HEAVIER WORKLOAD, INTERNSHIPS, JOBS, CLUBS, SOCIALS.....which is the situation I found myself in as college progressed especially my JUNIOR year, who knew that it would've been my LAST YEAR in COLLEGE...In a way I regret not making the extra time to hang out with the people I really cared about, and just focusing on what I had to do to get ahead in life. But should that be the priority? I'm not sure either. I regret not fully experiencing college the way it was meant to end..a time laughter and memories. I mean when will I ever be able to go to a free college sporting event, displaying school spirit? When will I ever get to screen free movies? Sadly I didn't take advantage to all that college has to offer, and I find myself here blogging about it.
The point is time is never definite. All of a sudden, I'm done with school and most of my friends are still in college, living up their senior year. Though I mentioned many of my closest friends are from back home, there are some at my college in which I miss dearly. Even though Irvine is barely a 40min drive (with no traffic) down south, it feels like a completely different world. It has dawned on me how much effort it takes to have a relationship remain, especially friendships. I have learned that in order for friendships to last, there has to be an effort from the parties involved. What happened to the people I would talk to on a daily basis, I barely talked to them over the entire summer going into this school year. Is that how post-college life is going to be like?
I guess in time you realize who are the friends that are worth keeping...