I know this girl, and we've been best friends for a few years. Our relationship is absolutely amazing.
We've tried dating before, but both times it didn't work very well.
However, I had just come out of a really bad relationship, and she was very busy with school, so there were several reasons, that were working against us.
Now it's been well over a year since then, and we're both still struggling with these feelings for each other and we don't know what to do about them. At this point, we're discussing dating again, but we're both worried that something could go wrong and we don't want to lose each other. But we also don't want to have these unresolved feelings for each other forever. We aren't really sure what to do.

Any advice would be greatly appreciated.

If it didn't work out the first two times, what has changed this time? Be sure to work out the problems that broke you up the first two times, otherwise, you're in for a third break up.

Why not take it slow with each other and see where that leads?

From my personal experience, I say don't do it. I started to date my best friend and it didn't end well. After we broke up things were completely awkward. We will never be the way we were. Now we don't even speak. Though if your feeling are really strong, maybe you should give it a chance. You should just know what you are giving up.

Yeah I don't think you should date a best friend cause if you guys broke up your friendship might not be the same I have done it and was not good so I say don't date him.