She cheated .

We have had our ups and downs and i really did think about leaving at one point but i loved her .
She has had problems before i met her she was raped before i met her, alcohol abuse and the day before i met her was at her best friends birthday she went with her man.
Her alcohol abuse was really bad i think she lost her first job because of this and i helped her she worked later for a factory which my mother was in a senior role i found her drinking in the afternoon.
After this she curbed her drinking and it helped.
She was flirtatious a couple of times with others and i thought no harm.
I found her one night with her bra strap undone at three thirty in the morning staggering up the road she said it was a dodgy bra cant remember getting up the road after a works night out.
The next time she was apparently at a funeral in a near by town and again never came home till late i was expecting her back when i returned from backshift and no joy she came home eventually when i was awake and i noticed her pants in her handbag i then thought wtf is going on i had access to her gmail account by chance as she had saved it on the pc and i was obviously thinking some thing is fishy was going on.
She met a guy that night and was chatting to him on match.com later?
I asked and she by chance met him a tennis loving, Ian Rankin person like her i moved on i had to trust her to be with her.
So that has been the last 15 years.
This weekend i had my family back to the house my sister invited her sister in law and man back and later under the influence he was caught kissing her in the garden.
Her mother died of cancer related issues last year which she had three times and she is putting her recent actions down to that.
She is at her fathers and im left feeling sucker punched in the gut i don't know if i can take her back .
Any advice please.