[anton]

Leave while you still have your dignity intact.
Like the brothers said, people don't hold the values you did when you were their age. Having read so many exploits of the brothers here, you should be able to sense that bf-gf and "i love you"s means nothing to younger people nowadays.
And the age difference makes the difference. Even if she loves now all the while till now, in just a few more years, when you hit 40 and she would just be a budding adult who will know a hundred more potential suitors, where would you stand in her life.
You are not her one and only anymore, just a back-up plan. It's like working at a job, all the while searching for a better paying one.
For her, I think it's just a case of Electra complex.