From the beginning of The Vampire Diaries, all the writers have done has praised SE e.g:
"This show is always going to be about Stefan and Elena. It has to be. They're soulmates."~KW
As a DE fan, comments like these have always lowered my confidence in DE becoming endgame or even getting together at all! So I've always tried to concentrate on the writers actions rather than what they say. And from that I can see that DE have to be soul mates or twin flames or whatever you want to call it. They can't be anything else. I've especially seen this proven this season.
You can't deny that SE love each other, and I'm not going to lie, they have a connection. Really, they are a lovely relationship. But from what I've witnessed this season they aren't as 'epic' as they are made out to be.
Season 3 started with Elena professing her love for Stefan and telling him to 'never let that go.' This scene scared me a little, I have to admit. I thought season 3 would try to prove how unbreakable their love is and display DE as a fling that would occur because Elena couldn't have Stefan. If SE were in fact soul mates then that is what [b]should[b] have happened. However my fears where ended as the season went on. Elena constantly tried to find the humanity in Stefan, tried to make him fight for it, showed him her love and loyalty as that something to fight for. No matter what she tried or attempted though, it didn't work. What did work though was Damon. Twice when his life was in danger Stefan's humanity showed with the help of Katherine once. Elena's quote from 3x08 describes this perfectly:
"I think that you're gonna be the one to save him from himself. It won't be because he loves me, it'll be because he loves you."
If they were honest soul mates, if their love was so true and 'epic' then the writers would have made it so that Elena would/was the one to bring him back from the edge. The writers would have shown us that their love is so strong, that his love for her would have brought him back straight away.
Then the final nail in the coffin(for me) which proved SE aren't soul mates is 3x09. It showed Elena finally letting Stefan go, accepting the fact that he couldn't be brought back(unknown to her, he kind of was but because of his brother).
"Then we'll let him go."
Once again, if the writers wanted to prove that SE were soul mates then they would have shown that Elena would never let him go. That she would keep fighting for him until she finally got him back. But she didn't, she realized that she had a life to live and she couldn't continue letting this love consume her. If he was her one true love, then she would have kept fighting for him. Also, this scene contradicted the scene at the beginning of the season. Elena told Stefan to 'never let that go.' but here she is saying to let him go. Nice parallel you got their SE:P
Now, on to previous seasons. This is when SE where shown to be their strongest yet I still seen the flaws. In season 2 when Elena was determined to die to save her loved ones, Stefan respected that wish. In many ways that would be considered a good trait, to respect peoples wishes. But when it's a matter of life and death, and especially when the one who is going to die is your 'soul mate' then nothing should matter but trying to save your loves life. I'm not saying Damon's actions in 2x19 were good or that I approve of them, it was irrational. But I'm sure if I had the one way known to save the person I love then I would sure as hell use it and deal with the consequences after. I'm not going to say that this proves Damon loves Elena more than Stefan, that is up to opinion. But if Stefan couldn't live with out her, then he would use every way possible to make sure she survived not just stand by as she goes on a suicide mission. When you love someone more that life itself, you fight for them and be reckless or irrational. Because nothing else should matter.
One of my favourite quotes is from Lexi which was later used by Elena to save Damon's life. "When it's real you can't just walk away."
Numerous times Stefan has walked away from Elena e.g 1x09 'Stefan don't walk away from me!' *Stefan continues to walk away* and 3x03.
In 2x19 Damon confessed to Elena he couldn't loose her to which she replied 'You won't'. In 3x07, Elena told Stefan 'You're going to loose me forever.'
Another parallel between SE and DE is this:
'I've been so selfish because I love you so much...'~Elena 2x06.
'And it's because I love you Elena that I can't be selfish with you...'~Damon 2x08.

In conclusion, to me SE can't be soul mates or epic which the writers love to force down our throats. If they were they would be written to show that their love is bigger than this earth and everyone around them. Stefan wouldn't lose his humanity and Elena wouldn't begin falling for Damon. To me, this is how it works...Stefan is Katherine's humanity, Damon is Stefan's humanity and Elena is Damon's humanity. They all help each other in different ways but that's how it ultimately is. No matter how the show goes on SE will never be soul mates or epic to me but DE will always be.

Thanks for reading:)