Maybe the person that stopped talking to you has his/her reasons idk whatever. Oh and even though the person is active it doesn't mean they're talking to everybody but you.
. . . This is me right now and I'm trying to act as if it doesn't bother me. But then I remember people get busy and actually have lives. And I'm like "oh. Oh." So it's not you, it's the circumstances.
And the fact that people probably click on the notification and then forget to reply, that's what happens to me and many others around here.