Writing Romance: How NOT to Do It

Perhaps I'm not the best person to be writing this guide with my indiscriminate hate for people my age and having zero personal experience with relationships of this type. But I do know real relationships. You learn a lot of things if you just sit quietly in high school and discreetly study people around you. (It's for research, don't you look at me like that.)
For me, a writer who twists the concept of romance so much that it's barely recognizable anymore, I have to know the basics of true romance. Can't screw it up if you don't know what the heck it is you're screwing up, am I right?

Let's first look at what defines a romance novel. A central love story and an emotionally-satisfying ending.
A love story needs to have conflict for the two people to fall in love. If your idea of conflict is "I don't have a boyfriend and no one likes me!", I suggest you start running before I find something sharp and pointy.
The characters need to grow. Not physically as in inches and centimetres, but mentally. Otherwise, the reader will put your story down.
Finally, there's the resolution. The problems need to be solved for the reader to buy the happily ever after.

Let's get on with the don'ts of romance writing.

Love doesn't happen instantly. That's infatuation. The online dictionary defines it as puppy love or temporary love of an adolescent. You don't really love someone you just met a few seconds ago. You haven't gotten to know them yet, so how can you? Maybe you've fallen in love with their appearance. 
Romeo and Juliet is a good example of this. Romeo fell in love with Juliet in seconds. Look where that got them. (If Romeo and Juliet was meant to be a satire, Shakespeare is a genius.)

You can't truly love someone without knowing them first. I think this requires no further explanation.

You won't die if that person leaves you. It's not like you suddenly share vital organs at that first glance and need them by your side at all times. You still have your organs, they still have theirs.

Hearts can't literally be broken into millions of pieces like glass. They're squishy and fun to poke. Don't even use this in real life after a break up.

Don't fangirl over the love interest. Please don't waste our time, only you have the perfect mental image. Whenever someone tries to describe a book character to me, this pops up in my head and I just stick on whatever characteristics you give me, such as this colour eyes and this colour hair.

Actually, if you've read any show vs. tell guides, they should've told you not to use these as the only descriptions. You're supposed to link appearance to personality or actions, something like that. I don't remember the exact tip.
Don't stick words like sexy/handsome/insert other adjective here if your only reason is JUST BECAUSE HE IS. Get. Out. Now. I'll forgive you if the MC realizes that the love interest is nothing but a pretty face and moves on to a guy with actual character.

Mary-Sues and Gary-Stus are a no-no in every genre. Again, no further explanation is needed.

I hope this entertained you as well as showed you what not to do if you're writing a romance novel.