Hello Your quarry is really interesting. With advance in science, now it is proved that there is nothing like Losing sex power by seeing porn films or masturbation. Semen is a common fluid as a saliva and a sweat it. You are having Premature Ejaculation , a very common sex problem. Can be managed well by medicines-can be available by prescription from psychiatrist. Few sex techniques eg women on top technique- doing sex in women on top position, Start and stop technique- eg taking pause during intercourse to lengthen the sexual intercourse may be helpful to some extent. Hope this answer your quarry well.