Hey there Ibi
It totally makes sense that online and offline (/IRL) you have different 'personalities'. This has to do with various factors, including that online you feel you can (more) control who knows what about you. Heck, you can even create a fursona and act all cute while maybe in real life you don't really want -or feel the need to- act cute. I don't want to linger too much on the why's and how's of that particular subject, but more on what I read is bothering you, which I can understand and I hope I can say something to help you with ^^
Is there anyone in real life, a friend or family member or perhaps any of your sisters (I don't know how old they are), who you can be open with and talk to? Anyone at all?
I'm sorry to hear your parents went through a divorce, especially one that didn't go so quick and clean. I think that would have saved you a lot of pain and worries. I don't know how old your sisters were or now, but they went through the same things as you did. I understand you had to put up a mask, though I cannot say for sure why. I can only guess it is so you could seem strong and supportive for your sisters.
But if anything, I think you can start opening up to them, talk about it to them, say you felt you needed to help them, support them. And that's why you were wearing a mask for protection, so you could do the things you wanted to do without breaking down.
That's what I believe masks are usually made and used for; to not show your true feelings. And judging from what I've read, you probably had an extremely difficult time. Try to open up to them, and see how it goes.
Don't be afraid, they are your sisters.
Take care, and most importantly: Don't feel afraid to be yourself. Not online nor offline.