if you have not done anything wrong my dear ,,, ignore them too ,,, human beings can change for no reason ,,,, move on and respectfully give then their space ,,for real the one who will come back looking for you ,, is the one to keep
I agree with @kui. 2nd situation is that person busy with another important work or some issue. sometimes we can not give space and relations close to one mistake. if that person does not reply to you without any reason. It's fine. this is a big world. wait and watch.