Welcome to the forum and thanks for your question. I'll try to help.
First, with her regular and recent STD testing, it is very unlikely your casual partner/friend has a transmissible STD. Second, most STDs are not efficiently transmitted; in other words, even when one partner is infected, the disease is transmitted only in a minority of unprotected exposures. Third, you used a condom for vaginal sex, which was really the only risky part of your exposure. Fourth, as just implied, oral sex is basically safe sex, with low overall rates for all STDs and zero for some.
Your symptoms don't suggest any STD. Here is another thread that discusses semen or prostate fluid being expressed during bowel movements. (It opens with a statement that this happens to "amost all men". That's probably not true -- but it certainly is a very common symptom.) As you will see, it's generally not a sign of STD or any other health problem. You can also find other threads about this by using the forum's search function.
http://www.medhelp.org/posts/STDs/Semen-Leakage-Question/show/684727
I cannot guarantee that you didn't catch something that you conceivably could have transmitted to your regular partner. But based on the information provided, the odds are very low. If I were in your situation, I would continue unprotected sex with my wife without fear of infecting her with anything, and I would not feel a need for STD testing. Of course you could always visit your doctor or your local health department for STD testing if you require additional reassurance.
I hope this has helped. Best wishes-- HHH, MD