once a cheat always a cheat?.

So around 3 weeks ago I found out my partner of 11 years cheated on me. (I thought everything was fine).
He went on a stag do abroad, had a one night stand with a girl then continued that affair when he got back home. He works away Monday-Friday. I found out he had met up with her 4 more times since the stag do, twice at the pub and twice he paid for a hotel and they slept together again. 
Anyway the only reason I found out was because we went to a wedding and I decided to drive so he could drink, we got back did the deed he fell to sleep and his phoned beeped..it was around 1am
So I looked, so I glad I did!. The said girl had sent him a picture of my Facebook profile with questions marks as if I was the other girl!!!. 
I confront him the next day he lies about who she is where he met her etc etc. Fortunately for me i new in my head something didnt add up I got her number and she told me everything!. Every last detail. 
He tells me he loves me it was one big mistake he did it for the thrill nothing else. We have a 9 year old child together, and only brought a house together 8months ago. 
I love the bloke and I feel so stupid and like an idiot for not telling him to leave. 
Has anyone else ever found out there partner had cheated and stayed around and it's worked out? Or does everyone think I should show him the door?. 
No nasty comments please my head is messed up enough. 
X
Update:
I'm still with him...not sure why, I must really love the bloke, and I'm trying to block everything out my head but it's so hard!. 
All that's going through my head is, was she better in bed than me!, did you actually have feelings for her!, do you still want to sleep with her!. 
(Bearing in mind we had a very healthy sex life, it wasn't like he wasn't getting it)
Does this get any easier!!? Anyone who has been in the same boat?. 😩😩

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