You caught his attention at a game early in the season.
And he met you after the game when you went to wait by the dressing room for your brother. Mat came out of the dressing room before Marty and saw you.
Mat had like an instant crush on you.
So he started flirting with you, and you found him hot and you knew he was a good player, so you flirted back.
And then Marty came out and totally did not approve.
Which is how Mat found out you're Marty's younger sister and he was super intimidated.
But, he still had feelings for you.
And you had feelings for him.
And you guys saw a lot of each other...
You guys started dating, but you decided to keep it a secret. You, or, more accurately, Mat, didn't want Marty to find out.
Marty is one of the league's toughest tough guys... Mat did not want to be on the receiving end of that.
You also didn't want Mat on the wrong side of your older brother's roughness...
But you guys suck at keeping secrets, so Marty found out after a few weeks, and boy... He was not happy that you guys would keep that from him.
He gave you a very disappointed big brother look.
And he gave Mat the glare of death and Mat received a very scary "if you hurt her" speech.
Since then, Marty did get rougher with Mat during practices.
Tito finds that hilarious.
"You're dating his sister; you get what you deserve."
You guys don't post much on social media, but there were rumors about your relationship, so Mat posted a picture of the two of you on his Instagram to confirm your relationship.
And the young Leafs (aka Auston and Mitch) totally comment on the post things like "he hasn't killed you yet???" and "praying for you."
Marty comments stuff like "you're both twelve stop."
He will throw shade at Mat any chance he gets.
The fans LOVE protective older brother Matt Martin.
Interviewers constantly ask Mat and Marty about yours and Mat's relationship.
There is no battle over who's jersey you will wear.
"Wear Marty's jersey. Just wear it. I don't need him checking me into the boards during warm ups if you're wearing my jersey."
If Marty ever catches the two of you doing more than light kissing, the next practice or game, he will slam Mat into the boards.
He's a protective older brother whose protectiveness knows no bounds.
But he does know that Mat treats you well and that you're happy, which is all that matters.
But he has fun terrorizing poor Mat, so he won't stop.