you may be causing "retrograde ejaculation" -- a condition where semen enters the urinary bladder instead of coming out of the urethra. is this safe? if this continued to happen you may have difficulty if you decide to have children. i am a primary care clinician not a urologist so it may be wise to consult a medical professional at this level.
i'm able to "stop" an ejaculation by contacting certain muscles in my pelvic cradle. i wonder if this is safe.