What does this mean?

I was away from my account for some time (maybe like 5 months) and that's where my few friends are on. I don't have their numbers and we normally text on like stuff like discord but they left that and I made a fb because of them.

Anyways I just got on messenger like yesterday after being away from Facebook and I texted my friends. It shows a blue circle with a checkmark with both friends in the messages I sent. One of them responded today when I checked. My other friend didn't respond and it showed they were online. Am I blocked or ignored or something? Or they didn't see it?