Hi, this is not a technical answer but this is how I understand it as a native speaker. We say ‘i am going to my friend’ or ‘i am writing to my friend’ as this implies time must pass for the letter to travel to them or for me to physically get to them in person. Texting is instant so their is no physical travel, be that a letter or me personally and no passing of time. So when we say ‘i am texting’ we do not need to say to, it is already understood. I hope this does not confuse you even more and is of some help. I am sure a professional teacher can explain this in a technical way but hopefully two different ways of explaining might be most helpful :)

Rebecca is correct. "Texting" can be a verb. Native speakers would say "I'm texting my friend." But it's not incorrect to say "I'm texting to my friend." It's more common that we would say "I'm texting WITH my friend." rather than "I'm texting TO my friend." although both are technically correct.

I'm texting my friend! Texting is a verb in English. You can say 'I'm sending a text to my friend' using 'text' as a noun but 'texting' is a verb.

I’m texting my friend.-correct Because it’s one of those phrase/ figure if speech rather than an actual verb Another example would be I’m skipping my friend And I’m skipping to my friend Two different meanings

Iam texting to my friend