I [25F] found 582 texts messages between my boyfriend [25M] of 1.5years and another girl, what is the best way to confront him?

I'm just going to dive right in and ask for advice on what to say as I have no idea how to approach this.
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Last night my boyfriend went for a night on the town with his friend Paul, I didn't hear from him all night which is not unusual as I tend to bother him when hes out with the lads. Paul rang me at 4:30am to ask if my boyfriend had got home yet, to which I replied he had not. The friend told me he wouldn't be much longer as he had just left him in town and that he was walking home (it's less then 2 miles).
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Boyfriend did not turn up and I was starting to get worried so I tried to call and text him but got no answer, he has a contract phone in my name because i'm stupid.
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I check on my account on the 02 website as you can see the texts/calls to see the last time he sent a text because I was starting to think something may of happened to him. I was scrolling through and recognised some of the numbers that came up but 1 stood out, he has sent 582 text messages to the same number between 17th April and 18th May. I thought that was an extremely high amount of texts to send, so I save the number in my phone and check WhatsApp - low and behold its a girl I have never met or know anything about.
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I have been re-reading the texts between me and boyfriend, 3 occasions between 17th April - 18th May he told me he was staying at Pauls house but when I have checked the dates on the texts he has been sending texts to Paul but not the mystery girl, so it is clear he has actually stayed at her house.
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He eventually called me an hour ago to say he went back to Paul's house last night, which i know is a lie because i was on facetime with Paul at 4:30am while he was walking home and he was alone. I did not say anything on that call and he said he would be home soon, I called him back to confront him but hung up as I want to do it face to face - he called me back just now to say that he is out having breakfast with Paul and that he would make his own way home around tea time ish (this strikes me as odd, thinking back he has always declined my offer to pick him up on these 3 occasions but every other time he will ask me to take him somewhere as he does not drive).
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When he comes back later today, how should i approach the situation? He currently lives with me, do i pack up his stuff? Please, any help would be appreciated
TL;DR - found 582 messages between boyfriend and a girl I don't know, I know but cannot prove that he has been with her on multiple occasions, not sure how to confront him
UPDATE: You guys don