Struggling as a step parent

I'm not officially a step parent since my SO and I are not married...but being together 7 years pretty much makes me another parent in his daughters life. The hardest thing I've had to come to terms with is accepting I will never share the same love and bond for her as I do with my biological children...and you know what? That's ok. As long as I treat her well and take care of her like my own that's all that matters.

Has anybody else struggled with accepting these feelings?