Maybe he's affraid of something (Like you getting pregnant) the only way to sort this problem is to talk about it and to "discover" each others bodies slowly and maybe talk about any worries he may have, but dont go in all barrels blazing, take your time, coax it out of him, there will be a reason, Maybe hes been hurt recently (Emotionally)

Okay: Physiological Reasons for Erectile Dysfunction Physiological erectile dysfunction happens when the erection is unachievable due to improper functioning of the hydraulic mechanism that pumps and retains blood in the penis. An erection occurs due to change in blood flow where involuntary muscles restrict the flow of blood out of the penis. Some of the physiological causes are: - Spinal Cord and Nerve Disorders (like Parkinson's, Alzheimer's, MS) - Hormonal Imbalances - Arterial Disorders (like hypertension) - Surgery - Radiation treatments - Lifestyle Choices (like obesity, smoking, drug and alcohol) - Age - Iatrogenic Causes (Medicinally caused) (like high blood pressure meds) Psychological Reasons for Erectile Dysfunction Psychological erectile dysfunction can occur when a man is feeling depressed, has feeling of nervousness or anxiety. The issue can arise from problems with work, family or money that can lead to stressors that can inhibit sexual desire and ability. Unresolved issues with a partner or feelings of self-consciousness are two other reasons a man may experience erectile dysfunction. One last reason may be fear of a partner's reaction. Rejection is a strong psychological reason to have performance anxiety. http://www.pharmagazette.com/2007/11/erectile_dysfunction_physical_1.html

are you using a condom??? sometimes it just happens cause he can't he can't feel enough through the condom. try either using sheepskin condoms or using a different type of contraceptive.