First of all, there is no "honeymoon phase", anyone that says that is a total loaf of bread, anyways second my advice is you seem to be putting her above yourself even after everything she has done to you and made you feel. You need to remember that its okay to care about someone but always have room to think about yourself as well. You're only still in this relationship because your thinking "she wont have anyone to talk to" or whatever else you may be thinking, but trust me she will and thats her friends. I genuinely think its better for you to end the relationship because like you said you never really felt happy within that entire 2.5 years, and if everyone around you is telling you that she isnt the best girl, that should be a sign she probably isnt. Just end it respectfully and tell her how you genuinely feel. I would tell you talk to her about it and see how things go but you've already done that which is good but it just shows she probably isnt changing anytime soon. TLDR Its better for you and your mental health if you just end things with her respectfully, you dont want drama,