Communication

Why is it that sometimes the closer you are to someone the harder it is to say some thing? Like 'I love you' or 'I'm sorry'.
Whenever I fight with my mum I always write her an apology note because if I say it out loud I run the risk of adding a but or starting things up again like a fool...
Whenever my ex and I talk about feeling we sit back to back or I lie on his chest because if we look in each others eyes its too hard to articulate everything we're feeling at once...
recently I've noticed I have one friend that its actually easier to explain things face to face because through email its too impossible to express everything you mean, you can't demonstrate, you cant inflect, you can't really emote.
Even the simplest of vague phrases require thorough explanation through any means other than talking.
I guess it doesn't matter what medium you're using to communicate the more important the person and the more important the thing you're trying to say you need to communicate differently to how you normally do; because something is different and part of you knows you can't just say it like 'pass the milk' or 'knock knock' or 'your mom'.