Have you ever been like this with previous g/f? Sometimes we get hangups that we just cant rationalise. I do think tho that you're on the right path to beating this, as you're fully aware. Have you ever thought about therapy to try and help sort this out? Perhaps even go with your partner if it helps. A therapist may help you sort out some issues or even try cognitive therapy so you are able to recognise the pattern you're in and with effort, stop it.

I do echo Leeds comment, please dont mess this up with stuff that doesn't matter and I hope you keep working on it. All the best to you both.