Let me clarify the behavior I wish, which is similar to mail apps such as yahoo mail, gmail, or the Mail app on a Mac computer.
There are 5 new posts since you last visited and the bell shows a (5) badge.
You click the bell and see 5 highlighted notifications listed at the top for posts 1, 2, 3, 4 and 5.
You click the link to visit post 3, reply to it, do a few other things etc...
The bell now shows a (4) badge.
You click the bell and see posts 1, 2, 4 and 5 highlighted, but 3 is now grayed out because you visited it.
That way you can immediately identify visually that you've already processed the notification for post 3 but you still have to take care of posts 1, 2, 4 and 5.
Does that make sense?