Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
I am very sorry to know about this frustrating and distressful situation.
Based on your story, I do not see you did anything wrong here, but consistently taken action based on what you knew about this person and his romantic situation, from what these co-workers shared with you, and directly from him. On the other hand it seems clear to me that he and this other co-worker have not been totally honest, open and direct towards you, and that's what led to this uncomfortable situation.
Please focus on taking full responsibility for your own feelings, choices and actions, which seem mature, assertive, respectful and sensitive, while he and this other co-worker need to do the same. The big difference is that they cannot feel proud for not being honest and respectful as you have been from the very beginning.
If his ex-girlfriend decides to confront you about what happened, you would also be totally honest and clear about what happened for her to see that in this situation you did nothing wrong, whole were misled by this co-worker and by his behavior.
Does it make sense?
Yes, it does. Thank you for your advice!
You're very welcome. Please feel free to contact me if you have any further questions and to follow up, since I am here willing to support you as possible.
You can contact me using this direct link to my profile http://www.justanswer.com/relationship/expert-rafael-morales-toia/, you could bookmark it for easy access, and just make sure you state "For Rafael only" in your request, for other experts to know you want me to reply, and I will respond in less than an hour most of the time.
Thank you for your trust. Take gentle care.