Right, hands up, being totally honest now, I was that friend.
Not literally of course, but yes, I used to be like this. In fact when I was going through the break up with the fat bastard ex, I was terrible, going on and on about it before, during and after ... and not really letting anyone else getting a word in edgewise or (to my eternal shame) it not even occurring to me that they might have news or problems of their own. 
What 'cured' me was when not one - but two, yes two of my dearest friends both fell asleep on the phone when I was rambling on!!! Separate phone conversations, they lived in separate parts of the country and didn't know each other, and the conversations were a couple of weeks apart.
I'm going on ten to the dozen, and suddenly in between drawing breath to launch into another diatribe about myself and all my woes ... I vaguely notice that my dear friend on the other end hasn't said anything for the last several minutes. Not even a 'yes' or 'oh that's terrible' a 'poor you' or even a 'mmm' or anything in the way of response. Then I realise there is some very gentle snore type breathing coming down the phone at regular intervals. 
I call her name, no response, call again .. nothing, shout her name down the phone and eventually she wakes up!!
The first time it happened ... I sort of laughed it off and my lovely friend was mortified and apologised profusely (although she had no reason to - I was that self-obsessed at the time I would have put a glass eye to sleep). But when it happened with a completely different friend a couple of weeks later, and once again I realised I was effectively talking to myself as my (male) friend snored away on the other end of the phone, it finally hit home how boring all this crap about me was to other people.
I'd put them both to sleep! And no, they weren't faking it - they had both genuinely nodded off I was that fucking boring.
I also came to realise that as kind and sympathetic as people can be - family, friends, acquaintances - people generally don't want to be around someone who is always talking about themselves and their troubles. There is a limit to how much people can take. I have a couple of narc nieces who drive me insane because they both think the universe revolves around them, and I can see now, I was in danger of going that way myself.
It was the kick up the arse I needed, and now I always make a point of asking and listening before I start talking about myself, and taking a genuine interest in what is happening in other people's lives. I also try and keep my problems and worries to myself for the most part and be more upbeat around people. If I've got the miseries for whatever reason I tend to just go into hibernation for a bit instead.