Help! my relationship is falling apart?

I am 29 yrs old. my gf is 32. we have been dating for 3 yrs. the thing is it is falling apart. there has been no i have been patiently waiting. thing is i dont know if she is using me. everytime we go out it is on my payday. I am always paying for everything and then I always have to help her with her bills because she is disabled. I have brought up with her but everytime I do she says its not the right time. I slipped last week and called a chatline. she caught me and got furious. nothing happened she just called me with another phone and i thought it was someone else. NOthing happened all I did was talk to a woman that night but nothing happened out of that. She calls this cheating and she wants to break up. My question is is she right? who is wrong here and what can I do?