Welcome to the Forum.  this was a low risk event.  Most CSWs do not have STIs and the "high end" CSWs are professionals who take better precautions than many other people at preventing and testing for STIs.  Your risk from this encounter, statistically, is lower than your risk if you had met and had a one-night stand with a new partner.  Further, as your partner stated, when condoms come off as a man is removing his penis from the vagina after sex, the condom has done its job.  Finally, why would this person not tell the truth?  Thus, to summarize, this is not an exposure that I would be particularly worried or concerned about.  Having said that, if you are worried there is no real downside to testing for the most common STIs (chlamydia, gonorrhea).  This latter statement about testing is not waffling - we recommend periodic (yearly or more, depending on the frequency of partner change) screening (testing in the absence of symptoms) for all of our clients with multiple partners.  It's just good sexual health maintenance.  The tests are affordable, highly accurate and can be done on a voided urine specimen.  No real reason for testing for other still lower risk STIs such as syphilis, HIV or herpes. 

I hope this is helpful to you.  EWH