A similar thing's happened to me as well. In high school, I hung out a lot which 5 other friends, and we got along really well. We spent time together during the school hours, and we'd hang out during the holidays as well and so on. It all changed when the fire nation attacked once we started university. We became different people and we started to have different interests - my friends became more interested in partying and so on, whereas I never enjoyed it. I no longer feel entirely comfortable in their company, even though we've never fought or had any conflicts. It's just mainly that I can't relate to them, and due to our interests, they don't bother to include me in their hangouts either.

I don't talk to them on Facebook. Of course if someone messages me, I would reply, try to have a little bit of small talk but also end the convo as soon as possible.

I do the same as well. I'm not hostile or rude - if they need any help, I'll be willing to try my best to help them out.

I guess the best way to reason this out is that things change, and people change. We all have to move on, and who knows, maybe moving on can help us to discover new things or new people.