my gf is trying to change her ex...what can I do?

well my gf said she knows she can change him and knows it is possible and won't give up....he said he was smoking playing on her sympathy...he lied to her...and he just keeps doing worse and worse things...as more issues more fights...but he won't help himself....so my gf is forced to help him more and more and try to change him...so she becomes more upset over him not changing and tries harder...I asked why do you help...she said idk I just have to help him and ik he can change...

she said she trusts him like 10% and doesn't care for him but because he has issues and hardly any friends....after 2 years because only she can understand him, she believes he can change...idk what to do...and he has his own gf he can speak to instead...each day he is coming to mine...she gets upsets and angry when he isn't changing, he just does worse things and things get worse :/