Should I break up with her? (Sort of long story)?

So I've been dating a girl for 2 1/2 years almost to the date. We met freshmen year of college and started dating within the first month. We broke up over the summer because she cheated on me for the 3rd time. We got back together at the beggining of the school year and things had been fine.
We just went on spring break, I drove myself, her and several of our friends to my beach house 11 hours away. On the last night she got drunk and had a 3-way with her best friend and my friend all over the house. Even when I approached them they did not care and continued.
The biggest issue is that her and I are currently in an apartment together and have signed a lease for an apartment next year with her, my self, my friend and the guy she had the 3-way with.
I just don't know what to do, I've tried everything and have done as much as I can for her. Any advice would be great!
Should I break up with her? (Sort of long story)?
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