Decided to break up with my girlfriend of 2 years

Problem/Goal: Broken up (20M) with my girlfriend (20F) because she speaks ill of my sister (29F) all the time.

Context: Nung namatay ang papa namin, yung manang ko ang sumalo sa pamilya namin. Dalawa lamg kaming magkapatid. After nya makapasa ng boards, nag work na sya agad para makapagsupport samin at mapaaral ako. Ang manang ko ang pinakamabait na taong nakilala ko. She never complains, never speak ill of anyone. Mapagbigay, family oriented. Kaya abot sa bubong ang respeto ko sa kanya. Nung pinakilala ko yung gf ko sa kanila 2 yrs ago, winelcome sya ng manang ko at ng mama ko sa family namin. Pag may gathering, lagi sya iniinvite. Kapag Christmas and birthdays, ang manang ko ay nagbabalot ng gift for her. Nag bake pa sya ng cake nung bday nya. Even bought her a labubu keychain nung nagpunta sya ng singapore. Itong gf ko naman on the other hand, always think na it's all facade. Feeling nya pretentious ang manang ko at wala daw ganung kabait na tao. Plastic daw ang manang ko at di nya feel. For the longest time, lagi eya may ganung comment and it hurst me every time. Iniisip ko lang na baka may turn around at marealized nya di ganun ang manang ko.

Nung December 27 was my last straw. Nagpunta kami nang manang ko sa sm and sabi nya pili daw ako ng shoes. Tingin daw ako ng dalawa at ibibigay sa gf ko. Ang sakit kasi hindi nya alam na binabad mouth sya ng gf ko. Tinanong ko sya, di din ba sta bibili ng kanya. Sabi nya saka na daw kasi bibilhan nya na lang ng automatic washing maching si mama. Sobrang bigat ng dibdib ko kasi napaka selfless nya.

After nun, nag chat ako kay gf na manang bought something for her para sa holidays. Nagreply sya ng "di naman ako nagpapabili"

And that was it. Mahal ko sya pero mas mahal ko ang manang ko. I can't let someone talk bad about the person who I look up so highly. The person who'd think of other people bago ang sarili nya. I love you, manang. And I am sorry.

What I have tried so far: Nothing yet. Naghahanap pa ako ng timing.

Please validate my decision.

edit: Thank you so much sa lahat ng comments. It warmed my heart and awaken my consciousness. Just passed by my manang doing sunflower crochets sa sala at niyakap ko sya. Asked me what's wrong and just told her I love her so much and thanked her for everything she has done for the family.

I will talk to my gf tomorrow and drop the bomb.