Oh, and in the meantime, your GF should know that you had a string of foster care placements and children's homes. Any lay person who cares would empathize with you; one does not need to have a degree in psychology to comprehend how attachment is formed in early life. So she should be in the know about your lack of stable structure for many years.

Treatment WILL help you, but... with time.

For right now, you need a stopgap measure - a temporary solution. If you find yourself saying those things to her again... and again... do not berate yourself but rather qualify what you are saying in an apologetic way.

"I know full well that you have done absolutely nothing - nothing at all - that could come remotely close to justifying any trace of doubt on my part, but I feel this this and that".

If you make sure that you hold her in high esteem and are only expressing your feelings without actually suspecting anything, I trust that it would be nice enough.

Or, to avoid lengthy conversations, you can come up with a code word and tell her what it means. Then your exchange might go like this:

You: the tornado is here once again
GF: oh, I am so sorry!
You: I am sorry for YOU since YOU have to put up with this
GF: oh well, I guess I have to (I think that would be the British way of saying it)
You: a hug?
GF: "sure" or "always glad"

And that is all.