Help?

So me and my partner have been togather for 3.6 years.. we have been on and off for things she has done to me.. hurtful things. 
Lying, cheating u name it .. I have taken her back so many times.. anyways we broke up for a month in June, and we didn't speak for that whole month .. then she texted me and we are back to where we are..
Anyways she hasn't told one of her friends she is back with me.. cause I have been asking her to tel her, so then I come come to girls nights to.. since I don't really have many friends and we used to al hang out before.
I am a girl by the way.
Anyways I have been saying why are you so scared to tell her.. well she just msged me today and said her friend has organised a girl night Friday , and I said oh cool, can I come? And my partner goes not this time.. I haven't told my friend .. I said tell her then?
Then she saids that her friend said if she ever gets back with me she won't be her friend anymore .
Now I just feel shit.. I'm nearly 25 and my partner is only 21. I feel like I'm to old for this shit... 
I said that it's okay, I don't want you to lose a friendship over me... we should just call it quits... I don't know how I feel :( thoughts?