It is HARD! I think its a skill that can be acquired though. I struggled with this badly for a few years, up until last year. Things that helped me, in case you might want to know: mindfulness, Buddhism, effort on my part (I had really made some mistakes in what I said online and in text that I regretted, so it was important to me), and talking to a therapist. I think journaling helped too. Like writing letters I won't send. I'm still not perfect at it. I told a guy off via text last May. Im a work in progress.

That being said, sometimes, I go from one extreme to the other. So now I'm more passive and like, don't always speak up when someone hurts me. I want to be more assertive. .

But anyway, I just wanted to say, I know what it's like and encourage somehow. Maybe also, don't be so hard on yourself.