You thanked the internet and texting for giving you a voice of sorts.
At least by text you could talk freely to your buddies without worrying about acting out what you want and need(which was a little frustrating at times). But even then, at least if you pointed at something or acted out well enough, people could understand you.

But you don't think there's a proper way to 'say' "I love you". At least, not to Karkat Vantas.

You've liked him for a while now. He's a good friend of yours, and while he's extremely cranky, he does have a soft side to him. He pities you because of your speech disorder, and does his best to help you. But even he knows that just because you can't speak, doesn't mean you can't irritate him sometimes when you get smart with him. He is mostly kind with you though and helps you out whenever you want something(he just plays it off as 'one of his duties as a leader') and you appreciate him for that. Sometimes you even give him small kisses on the cheek when he's being extra nice.
You're not sure if Karkat likes you back or not. Maybe the signals were there after all, but you didn't quite catch onto them. Either way, you decided(after a very long 'talk' with Rose) that you should just 'tell' him how you feel today.
To your luck, he was online on Pesterchum.
--[chumhandle][C/H] started pestering carcinoGeneticist[CG]--
[C/H]: hey, Karkat?
CG: OH, HI. WHAT DO YOU WANT?
[C/H]: are you doing anything at all today?
CG: NO, NOT REALLY. I DON'T HAVE A LOT TO DO BESIDES SIT AROUND AND GET BOTHERED BY GRUBSAUCE-GOBBLING IDIOTS ALL DAY.
CG: NOT INCLUDING YOU. THOUGH YOU'RE STILL PRETTY ANNOYING SOMETIMES, IN THE NON-VOCAL WAY.
CG: ANYWAYS, WHY ASK?
[C/H]: haha, well...
[C/H]: I was just wondering if we could go to lunch, maybe! My treat to thank you for helping me all this time.
[C/H]: hope you don't mind telling the waiter what I want, though.
CG: SURE, WHY NOT.
CG: WHERE ARE WE GOING, ANYWAYS? SOMEWHERE FANCY AND SO EXPENSIVE THAT YOU'LL HAVE TO DUMP OUT YOUR ENTIRE WALLET TO PAY FOR?
[C/H]: no, just a cafe or something simple! oXo
CG: ALRIGHT.
CG: SEE YOU AT YOUR PLACE, THEN?
[C/H]: definitely!
CG: OKAY, BYE.
--carcinoGeneticist[CG] ceased pestering [chumhandle][C/H]--

Your heart fluttered a little. It was nothing special if it was in the 'friend' way, but to you, going on some sort of a date(if it could even be called that) with him was extremely special. You just hoped he wouldn't turn you down, though the possibilities could be 50/50.
You were looking in the mirror and fixing the last parts of your hair when you heard loud knocking at the door. It was just like him to knock like that, you thought to yourself as you rushed over and opened it to reveal Karkat in a grey short-sleeve tee and black knee-length shorts. You were in a white tank top with a denim skirt. He took a look at you and said, "You look great." You couldn't think of any possible way to return the compliment, so you just smiled. You held out your hand and he took it, starting to walk as you closed the door behind you.
You reached the cafe and took a seat. You both ordered sandwiches(Karkat ordered for you, of course) and ate well. As soon as you were both finished, you 'asked' if Karkat had a pen by making a writing motion with your hands and then pointing to him. He looked at you inquisitively for a little bit and then got what you were trying to say. "Oh. Yeah, I have a pen somewhere..." He digged into his pockets and pulled out a ballpoint pen, which you took along with one of the napkins. You immediately started to write on it.
{Karkat, I have something I need to tell you.}
He looked at the note, and then back at your face. He always tried to search your face for emotion, because it helped when understanding you, but your expression was a bit...strange for him to tell what it was. It seemed to be a mix of desperate and shy.
"What?" he asked, confused. You turned the napkin back around and scribbled feverishly on the napkin again, your face growing hot as you covered it from his view. As soon as you finished writing(you had to unfold the napkin a little) you turned the napkin his way, put down the pen, and looked at your feet as he read.
{I've had feelings for you for a long time. You're extremely kind to me, and you help me out more than the others. Even if it is just 'part of your duties as a leader', thank you. It's okay if you don't like me back and all, but I appreciate that you take your time with me, although I might annoy you sometimes. I just really love you. Thanks a lot.}
As soon as he finished reading, he looked at you, and in a quiet voice he said, "[Name]."
You looked up at him shyly. He had the softest expression you'd ever seen him with.
Suddenly, he grabbed your tank top, pulled you forward, and kissed you. He broke away after about 3 or 4 seconds, and looked at you. "[Name].[Name], I- I love you. I guess I've liked you for a while as well, and I..." He let go of your shirt, leaned back in his chair, and looked at the ceiling. "I guess I'm really fucking happy that you like me back. You might not be able to talk, as annoying as it is sometimes, but I love you anyways."

You grin from ear to ear. Karkat Vantas may be blunt, but he's your boyfriend now (oops- you mean matesprit) and you love him to bits.