Thank you for writing in tonight.
At this point, you took the proper precautions to prevent a Chlamydia infection; however, this does not mean that it was impossible. There may have been a problem with the condom, or perhaps there was some secretions introduced into the urethra during the hand job. Also, this may have been contracted during other sexual contact, perhaps with your girlfriend. I do not know how long you have been with your current girlfriend, nor do I know your past history together; however, since you were protected during the encounter described, other sexual interactions should be considered. Regardless, at this point, both women should be told and tested. I realize that you cheated, and you do not want to tell your girlfriend; however, it is necessary, especially if you have had sex with your girlfriend within the last couple of weeks. Women and men can have Chlamydia without any obvious symptoms. It is so important to talk with both women, due to potential risks. If left untreated, STDs can develop into pelvic inflammatory disease and even infertility.
I hope this helps. If you have any additional questions or concerns, please let me know.