Don't feel guilty, or I need to start feel guilty... I'm exactly the same, or even worse. I cut people out of my life just out of boredom. I fail to even remember their name after short while. For some time I also felt extremely guilty, now I fail to do that too.
I noticed, that when I met someone (not important to me kinda person) that I didn't actually even once ask how they were doing. I just answered to their questions very briefly and didn't make any counter questions.
The funniest part for me is when people do this with high pitched voice "HEEEEEYYY, Let's stay in touch, don't be a stranger" and both sides of that party know that is a lie.
Ahh glad to know I am not the only one struggling with this (even though I am not glad it makes us feel so shitty)...I like to think that some people come to our lives just like chapters - they have a beginning and an end, and it's no use to force it if you just don't click together. I am able to keep contacting people who really matter to me which makes it all the more painful when THEY are the ones who don't reply. It's really shitty to be at the other end of it, which is why I would like to improve in that. What if I make people feel shitty with my non-actions?
You're totally right with the last comment - it's even worse when you run into those people months later and don't even know if you should say hi