Boyfriend left me for a girl from work, will he come back?

Me and my now ex have been together for 1 year and a half. We moved in together last August and it was good. We always got on so well and had a great time. In January, I noticed that he was messaging a girl from work quite a bit, who was newly single, but he always assured me it was nothing. Anyway, we had a few arguments about it and 3 weeks ago he turned around and broke up with me because he said he needs to be single. Turns out he had kissed her a month ago but said he stopped it.
Since the break up, he has been living in my flat as he couldn't find anywhere else. I got in a new roommate and gave him a date to be out by. He started messaging me random bits when I was out, was still couply with me and started doing things like buying me breakfast. Anyway, his last night, he showed me something on his phone and I saw a load of messages from her come through. I confronted him, he cried saying that have arranged a date but it's only a date. He said he doesn't know what has happened to him, he might be making the biggest mistake of his life and hopes this is just a blip.
He left his passport here and has messaged me about that, told me his new flat has fallen through and has apologised. I only replied to logistical messages and gave his passport back, but not in person.
I don't know if I want him back but I feel angry about the whole thing and want to know what are the chances of him coming back? I have met this girl from work who cheated on her boyfriend with my ex's best mate (sleeping with him) and cuddles up to another of his married mates on our sofa. Any advice on how to act - is cold shoulder the best for now?
Boyfriend left me for a girl from work, will he come back?
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