What the hell is wrong with him?!??
He asks himself the same thing, he had for months, and the answers aren't even answers, just vague speculations. He's a fearless ninja, a leader, a warrior.... and he gets so damn weak every time you pass by.
It started the moment he laid eyes on you. You took his breath away in less than a second, his heartbeat was so fast that it was almost as if he was running a marathon, and since then, he's been madly in love with you.
Everything about you was perfect to him, even what could be considered flaws, but he just couldn't comprehend it due to how strong his feelings had grown, you just drove him crazy with one glance he stole from you. That's how much he's fallen, that's how fast he's loved you.
Everyone could notice the effect you had on Leo, how you had him wrapped around your finger so easily, and yet, you were as blind as a mole. And to your defense, Leo got too nervous to make a move and court you.
With guidance from Splinter, advices from April and other female friends who I won't mention because I haven't finished reading the comics (I apologize for that btw), he started courting you and flirting with you, tho he did mess up a lot because of how nervous he got, but he stayed confident.
He would be a gentleman, opening doors for you, complimenting you, giving you flowers, all the stuff he was advice to do, because even if he had no experience with love...
For you, he would do everything to win over your heart.