I need to break up with my fiancee, I can't take it anymore!?

Im 29 and have been in a relationship with my fiancee for 8 years and have been engaged for 3yrs, she is 26. I am a firefighter and work shift hours and she has a full time job also. We haven't been getting on that great since the start of the year, She comes from a large very dysfunctional family who are alcoholic's but also work on the job, Many of her family can't keep a relationship or a marriage as they have all either left their partners or cheated on them. She was really rebellious when i met her but she tries so hard to be the opposite of her family and work really hard to get her career. Im in love with her so much but i can't stand the fighting and tension anymore, I've asked her to try counseling but she says we don't have the money and we don't need a third person sticking there nose in that we can work on this together. She is like her family and can be very stubborn and really hot headed, we have had screaming matches a lot and then she breaks down crying saying she can't take this anymore and i try so hard to cheer her up. We still make time to have a sex life. I play in a band sometimes and i dedicate songs to her and if she is pissed at me i always play her a song about how she pisses me off, then she turns on me or walks out. The other day at the firehouse i asked her to drop me in something i forgot and she brought the wrong thing and i told her she had a 2 second memory and she pushed me & told me to f*ck myself and left. I love her with all i am but i can't do this anymore i need a break from all this crap, I know this probably sounds horrible but i want to make love with her one last time before i break up with her, I need some opinions on how to end this without hurting her too bad!?