What the f' was that?

I understand fights. I grew up with fights and arguments and disagreements. But I thought you resolved things by, well fighting.
I didn't have a lot of fights with my friends as a youth. My sister and I fought a lot, but almost never silently. Now that I'm an adult I have had 2 of my friends mad at me. Both have responded in the same way by NOT saying a word. I only find out we've been fighting much later. One of my friends, who lived far away, told me 5 months later that she was mad, had been avoiding my calls, and I had offended her. I was crushed. I thought everything was fine. She and I would often go for months without actually speaking. How was I supposed to know?
This time it only lasted 15 days. I thought it was odd that she didn't get back to me after I gave her the Baseball tickets, or return my call when I told her I had brought back a gift when I was out of town, or when she didn't respond to my smartass texts, or when I left messages telling her I was really worried about her because I hadn't heard from her in a while. Turns out she's mad at me... because of 2nd hand information?

Ah well. What can I do? If there is no one to talk to about it, there will be no resolution.
But I get to feel really, really bad... and Hey, I visit my sister this weekend too, so that will be fun.

Here is another installation of crazy letters.

I guess I need to explain to you how much I don't appreciate hearing
comments that I can only take as judgmental and snide (going on past
statements and actions on your part) from your sister. I am really disappointed that you seem to take pleasure in judging me when I am going through one of the toughest times in my life. To hand it back to you, I really don't think you are in a place to pass judgment on who people love.
I am sorry my behavior doesn't meet your standards, but you have judged and embarrassed me enough. Let's remember you once sat one Dave's lap and started to unbutton his shirt right in front of me once...but he's an asshole!