Girlfriend can't be herself in our relationship

[Wheretogo113]

Hi, I really would like some advice please to whether I'm being heartless. I have been in a same sex relationship for almost 3 years, and whilst it hasn't always been easy due to us both having mental health issues from past trauma, we were both 100% committed to building a life together.
Anyway, in the middle of a row last night, I asked her if she had began to think about us separating, and she admitted that she had. I was very hurt and she immediately started to backtrack.

We have spent all this morning talking, and she has admitted that the last few months, since beginning therapy, she has realised that she cannot be herself in our relationship, and that if she cannot change this, then she would rather walk away in the long term as life is to short. This is a problem she has had in all her relationships, and has caused us a lot of problems as she tends to lie to avoid conflict. I was very supportive of her going to therapy, and have been paying for it to enable her to go, but this has really shaken me and I feel like all the grounding I had in the relationship has been ripped away.
I feel like I have spent 3 years in a relationship where I grew to love this person and have heard her repeatedly say to me how happy I make her and that she could never imagine her life without me, and now I feel like that was all lies.

She is very upset because I have told her how hurt I am, and that I feel I need space from the relationship whilst she decides what she wants. She has told me that she needs my support with this to help her change and become the person that she wants to be in order for her feel that she can stay in the relationship.
I am angry, and right now cannot give her that support, knowing that she has one foot out the door.
She is adamant that it is a good thing that she has recognised that she needs to change, but can't see why I am so hurt that our relationship may be thrown out the window in order for her to achieve this. She can't see how that has ripped away so much of the security that I felt with us.

It would be one thing to come to me and tell me how she wants to change stuff about herself as she is struggling, but that it has no bearing on our relationship, but quite another to tell me that if she can't change than she feels like she wants to leave and be by herself. I understand that she must do what she needs to, even though losing her would hurt like hell, but am I heartless to need to step back to protect my own heart now that I know our relationship is out the door if she can't change and be more happy in her own skin in a relationship?

I would really appreciate some gentle but honest advice please

You've done more than enough by supporting her emotionally and financially with therapy. And second of all of course you have every right to step back if she saying she is still deciding her position on the relationship. Being with someone while they do that leads to second guessing and paranoia. Its not healthy.

I guess though, you're saying she doesn't understand why you're upset etc. Have you double clarified this is what she means?

Thank you for replying. She says that she doesn't understand, but I think she must do and is just not being honest now, which she has done many times, although since being in therapy, she is a lot more truthful, hence admitting she felt like this I guess.
She has said that she can't imagine her life without me and is arguing that her feeling that she will need to be on her own if she cannot change, is very different to her saying that that she will leave the relationship. Well that makes no sense and is completely contradictory. She has never felt like she can be herself with anyone, and I know that has had a devastating effect on her mentally, but surely it is not right to feel that I should support her whilst she feels like this, and have no regards for what I feel has been ripped from me in terms of grounding and security in the relationship?
I hate that I may be being heartless