there are two theories with no supporting evidence behind either one so its imposable for me at this point to medicaly answer this concern. crying during or after sex or masturbation is widely experienced and even referenced in a few major films, however the cause of it is completely unstudied. One theory states that it is caused by hormones being releaced, estrogen in high doses can cause depression, testosterone can also cause a sense of being emotionaly overwhelmed which the body can manualy shut down by crying. the other theory is that crying signifies stress in connection to openness with a partner (or self),suggesting that there is an underlying problem with the relationship causing a lack of trust or understanding.