About Alex.

I will not take any criticism.
Let me make that perfectly, undeniably clear:
You Will Not Shit Talk My Boyfriend.

Besides the fact that you have never met Alex, and therefore have no basis for your dislike of him, your contempt stems from that fact that he's in a fraternity.
Grow up and go to college.
The Greek system is really fucked up. I've met several assholes from other fraternities, and don't even get me started on the sororities, but One does not mean All and just because they are perceived in a certain way doesn't mean that they are a certain way, and the thought that you would go around haphazardly labeling things like this has got me very upset.
Because Kappa Sig has thus far proved to be the exception, and not the rule. All the members I've met have been polite and have welcomed me as part of the group without question, based purely on the fact that I'm their new little sister. I'm investing a lot of time and emotion into becoming a part of the unit, and I've so far had a lot of success.
I really like them. They're really good guys.
None of them are the stereotypical, meathead, fratboy.

But, besides the fact that your nastiness is misplaced, why is my relationship any of your business?
I'm not your girlfriend. I'm not even your ex.
In fact, I have absolutely no place in your life.
We have never meant anything to one another, besides a sort of uneasy friendship.
Your newfound concern for my dating life is probably based on what you wanted and couldn't have (ie: unrequited feelings.)

And I get that. Really, I do.
However, that doesn't excuse your behavior.
My "douchey, alchy, jocky fratboy" is my boyfriend.
Whether or not he actually is a jock or a douchebag (I'm not even sure what "alchy" means,) is none of your business, nor is why/ how I came to be dating him.

Alex is super important to me.
He is, without a doubt, the best thing that could happen to me at this point in my life.
I don't know how to express that without sounding like a lovesick teenager, because that's exactly what I am and I am happily embracing it.
We will probably not be together forever. We probably won't be together for a very long time.
But, while we are dating, I expect you to respect our relationship.
And you should expect that I will defend it to the best of my ability, especially when the attack is invalidated.

tl;dr: Get your fucking nose out of my business, Taylor.