So I guess, he or she is with someone else?

Text message. Or that

Seeing an Instagram post of your girlfriend facetiming with her new boyfriend without her even telling you that she had any intention of ever breaking up.

The insta post is hilarious!

On FaceTime

Some of the guys in my class in high school were ruthless, texting their girlfriends on Valentine's Day

While being murdered.

Why would they wait until Valentine's Day?

Text message, Valentine's Day, birthdays...
New Years Day maybe?

When the person cuts all ties with you without officially telling you it's over.

through text first break up too... I made it into a Sims show too, my ex is is sure a loser in that show.

The dude isn't even hot or good looking. Leave his ass sis.

deliberate cruelty.

This or finding out from someone else that they dumped you

Finding out by someone else

Finding out through someone else?

OR

This guy I was seeing (not a boyfriend, but still I thought it was going somewhere), invited me to his birthday party (I assumed I was his date), and when I got there he introduced his new boyfriend. I died a little inside