Thank you very much for the additional clarification.
In order to make a definitive diagnosis or estimate of your issue, it would require a phyiscal examination by a urologist or GP, where they can also take any necessary lab tests.
In my opinion this seems to be related to non-specific uritis, or more likely a chronic prostate infection. A prostate infection can occur quite innocently from having a undetected or incmpletely treated cystitis or urethritis that progressed up to the prostate gland, as sometimes occurs. it could occur from minor innocent incertion errors during intercourse, where germs got introdued to the urethra.
The prostate gland is the source of seminal fluid that contains the sperm and when you have a bowel movement, if the prostate is infected or enlarged, there is pressure placed on the prostate that causes some leakage.
While there may be other causes than prostatitis or enlarged prostate, that is where you and your physician should begin. These conditions are benign, and are easily resolved with medication, and drinking plenty of fluids.