Oh, I can differentiate between the two. It’s super easy because I have a brother. He’s 5 years younger than me. We’re close but our relationship is completely sane, thanks. I spent pretty much this whole weekend with him and his gf and my husband and I can give you a whole bunch of ways we’re nothing like Sam and Dean. For instance, not once during this weekend did either of us gaze at the other like this: 

And as shocking as it may seem, we spent all that time together and yet rarely found the need to stand right on top of each other. We enjoy our personal space. I’m saying we don’t go in for this type of nonsense: 

We rode on an elevator and this didn’t happen:

Not once did he signal that I should look at his crotch like so:

Neither of us have broken up with a romantic partner for the other. 

Never has he been in trouble and I decided to kill myself to bargain with reapers. 

I did sell my soul for him once… oh no wait. That was Sam and Dean. 

See, my brother and I? We’re just normal. Ordinary, boring people. We’re NOT Sam and Dean. There is nothing normal about them or their relationship. 

So yeah. I have no trouble differentiating between fiction and reality. Seems like that might be a huge problem for you though. You obviously cannot tell the difference between the fantasy world and the one we live in. I hope you get help with that.