I saw a high-end escort who has been in the industry for 5 years and used a condom for penetrative sex but received unprotected blowjobs.  The second time we were having sex the condom had slipped exposing half of the penis shaft but the penis head was still covered at all time and she readjusted the condom to cover my whole penis. I cummed in the condom and removed it myself also peed 20 min later.  After coming home I noticed white flakes on my boxer briefs, scrotum and small flakes on my penis head and 1 white flake inside penis opening. 

Would it be possible for me to get any STI if her vaginal fluid (grool) got inside the condom during sex or while she was pushing the condom back down my penis???

She told me she gets tested regularly and had an incident where a client had accused her of giving him gonorrhea and she replied with her recent negative STD tests.

Welcome back to the Forum and thanks for your question.  I'll be glad to comment.  Congratulations on your commitment to safe condom-protected sex, it will do much to keep you safe.  When a condom covers the tip of the penis it will do the job you want it to do-protect you from STIs, should your partner happen to be infected.   There is a theoretical concern that, as a condom slips down, if your partner has herpes or another lesion disease such as syphilis, you could be infected but this is really extraordinarily rare.  

I would not be worried in the least about any STI as a cause of the white flakes you have noticed.  The most common causes of white, flaking lesions are fungal infections or a non-STI dermatologic problem called seborrheic dermatitis.  

I hope this comment is helpful.  EWH