I have to echo what others have said. His story doesn't make sense.
My XWS did something similar. He went on a business trip with a coworker and shared a hotel room. I figured it out and confronted him when he came home. He gave me the same story he told you (that his business made them do it and he didn't tell me because there was nothing he could do about it and he was afraid it would make me upset).
Ironically, I think the coworker turned HIM down. They were close friends and she got him the job. We'd go out to dinner together, etc. After that trip they stopped talking to one another. She told their boss she didn't want to work with him anymore and stopped taking his meetings. He told me it was because she was incompetent and jealous. I think I know what was the real reason now. I hear that after DDay and our breakup things got so bad between them someone reported him to HR as "hostile" and he was forced to move his office into another building.
He eventually moved on with another divorcing coworker when I was out of town for work... So that first incident with the hotel room and the other coworker was just the tip of the iceberg.
I NCed and left him before I found out more. That was all I needed. I was strangely lucky because when I uncovered everything he got defensive and hostile and the NC became mutual. Otherwise, if he were truly remorseful, I don't think I could have ever walked away. It's taken 7 months, but I now see that this was a terrible M. I was just too wrapped up in my own career and FOO issues to see it.
Best of luck to you. :/