Wrap content text around sidebar. Help, please!

I’m creating a template (my first one), and I’m working on my single.php file. What I want to achieve is something like THIS.

Here is my SINGLE.PHP code, and here is my STYLE.CSS code.

So far, the right sidebar is exactly were I want it, but the left one stays UNDER the_content. If I push it up by tweaking the margin thingy, it gets to the position that I want it, but the_content stays unmodified under, meaning, it doesn’t wrap around the sidebar.

It’s driving me crazy.

Thanks in advance!