Dear user, Thank you for writing. I understand your problem and its related concern. Masturbation is a normal healthy way of sexual satisfaction. It does not cause erectile dysfunction. You described losing erection just prior to penetration during sex with your partner at an occasion. This is common at your age but, do not feel down. Erection dysfunction (ED) is most commonly caused by psychological issue known as male performance anxiety. (One s excessive concern about quality of erection during sex) Erectile failure does happen sometimes to every man due to functional or situational reasons like fatigue, tension or own pressure to perform rather to enjoy sex . This is as common as common cold. This reduces sexual arousal and hence erection loosens. This failure of erection makes one feel I should perform best next time and he tries to erect’. For constant erection, continuous erotic thoughts, feelings of sex, joyful feel, joy of being touched and caressing (kissing, fondling) by partner, sexual fantasy, seeing partner enjoying sex etc should go through one s mind. But, if mind is diverted to concern about quality of erection and performance then erection loosens. Just enjoy kindling and joy of touch by exploring the partner s preferences of sex and share your preferences of pleasure with partner. Do not bother about quality of performance or erection during every sexual act. Practice this regularly. Relax and go ahead. I hope this will help you. If you have additional questions, then please feel free to write. I will be happy to answer your questions. Wish you good sexual health ahead.