How to explain to her that it really isn't that great?!

I understand how you feel, although I can't say I've ever had a boyfriend. I've had friends before who were heartbroken over boys breaking up with them, and I've comforted a lot of them.
I think you should just stop trying to explain things to her and let her experience it naturally. When she has her first boyfriend break up with her, she will understand. Until then, just try not to lose your patience. (I know this is easier said than done.)
Also to anyone who feels the need to comment, she means that sometimes you can feel so upset over a breakup that at the time, it feels almost similar to mourning a death. Don't take offense. ;)
Good luck! I hope this helped. :)

Its called life. Get over it.. Geeeze.. Wait till your 38, married, kids on your hip, house bills and car payment, THEN he dumps you ....!
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Death.. End of the world .. Bull crap,, At 14 you know squat - relationships can be more stress than they are worth, getting over being dumped is essentially mourning a death - Hon, gimme a break. You know NOTHING yet and haven't a clue on what is out there..
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oh you 14 year olds are clearly so mature. ok first of all, I agree with the girl up there, getting dumped is not like mourning a death. That was a very stupid thing to say. Second of all, who cares. You're both probably in middle school. Relationships shouldn't even matter to you guys now.

Getting dumped is not like mourning a death.Never say that again

You are a 14 year old girl with a whole lot of high school ahead of you. Your friend will realize herself and when her time comes to get a boyfriend, she will experience it for herself. let her make her own mistakes. You can't tell her boyfriends aren't worth it just because of your past experiences, you will find someone too. you have to get through the losers to get to the winner. Everyone has had to do that. Good luck ;)

me!

Just about everyone gets into relationships, and yes, they can be frustrating at times, but they are also rewarding.

She's looking at you being in relationships in an envious way, because she hasn't experienced one yet. It's the "grass is always greener" syndrome.

And you need to know that even though ending a relationship is heartbreaking, you can (and do/will) get over it. Once a new guy enters your life, the old pain will go away.

As to how these guys "dumped" you, they need to man up and grow a pair. What a bunch of cowards!

You have to keep in mind that she doesn't have a boyfriend, and that she hasn't had one yet.
She is using common sense to try to help you.
She IS your best friend after all, so don't get too pissed about it.
Just calmly tell her that it's hard for you to get past relationships with people you cared so much about.
It feels like throwing away months and months, and possibly even years, for some people, of love.
But then again, doesn't this quote pop into your head from time to time...
"Better to have loved and lost, than to have never loved at all..."
But never, EVER, say something as rude as...
"YOU DON'T GET IT! YOU'VE NEVER BEEN IN A RELATIONSHIP SO YOU DON'T UNDERSTAND!!!".
Tell her that losing someone you love is very hard.
Good luck :)
And good luck with your relationship :)