Gently, married men who post profiles on dating websites do so in order to arrange sex with women other than their wives.
This one girl? Maybe she's telling the truth. Maybe they didn't meet.
But is she the only one he contacted?
You need access to his online accounts---email, online dating services, and so on.
Do not give him time to scour them clean---if he does not immediately offer transparency immediately, it is a HUGE red flag.
(My husband waffled about transparency. Histrionic to the hilt, he declared it was akin to "Giving up my SOUL!" I think his "last" OW--who he cheated on, too--provided him with that line. Anyway, the waffling came to an end, and he provided passwords---to accounts from which he'd removed ALL information. Except for one little email in the trash he forgot to delete---which gave me a good picture of what was going on. He never offered any other details---so without that oversight, I'd still be in the dark, wondering why I was so broken I couldn't see all his hard work to be a model husband.)
But I digress. My point is that for every ice floe you uncover, there's quite often an iceberg below, and I suspect there's more to the story than what you've been told.
In my experience (and my husband long preferred anonymous hookups from online sites---the "last" OW was as much a stranger as anyone, only they built up a fictitious past), it takes a while for a married person to move from online banter to sexting to phone contact to meeting in person.
I mean, it usually takes more than one woman.
I'd be very interested to know the extent of your husband's online activities, as well as his texting and phone habits.
Do you have access to cell phone records? Those give a wealth of information. Text history is also useful. If deleted, it can sometimes be recovered.
I'm so sorry you're facing this---and so sorry to be the biggest buzzkill--but suspect there is much, much for you to discover still.
Millions of hugs to you.
ETA:
I have all his passwords, we've always had eachother passwords to everything.
Gently, no. You don't. Until he gives you passwords to Ashley Madison or Adult Friend Finders, or whatever online hookup sites he's using when out of town, you don't have all his passwords.
Given the history, I'd be pressing my husband to insist his employer have him work from home, or I would move to where he works, out of town, or I would insist he find another job. Clearly, he's not behaving like a married man when he's away from home--and that must end.
[This message edited by solus sto at 12:21 PM, August 16th (Friday)]