Whinnie the Pooh had it right - he got it. Nobody know how we are feeling unless we tell them because nobody is in our heads except us. For Whinnie the Pooh it was how cold his toes were growing - I have always wondered why he didn't tell anyone how cold he was, but he didn't, so nobody knew!
How do we know how someone we love is feeling? The straight forward answer is, we can't. We simply can't know, unless we ask and they choose to tell us.
What if they are really hurting and we can see that? What do we do then? There are many things that maybe are what not to do. Very high on that list is saying "I know how you feel". When someone says that to me I can almost feel myself screaming inside "You don't. You can't. How can you possibly think saying that helps? Leave me alone!".
But if someone does say that, maybe it would be more helpful for me to think "this is my friend who is trying to help".
What do I say if someone near me is hurting? I try really hard to say something along the lines of "I don't know how you feel but I'm here for you and don't know what to say".
The reason I think that's a good idea is what happens when I'm hurting: someone just being there is often enough. It's an indication that I'm not alone, that someone cares for me enough to sit with me (in person or remotely) even when (or maybe particularly when) they don't know what to say.
And what about the people who don't know what to say and so ignore what is happening? For me the only thing to do is to name that - to say something to them along the lines of "I'm having a rubbish time and need that acknowledged. I know you don't know what to say". If it's a real friend, that will be enough. If it is one of those one sided friendships we all have and they don't like hearing that, then we know where we are with them. So that's a success too.