Sorry to hear about your difficulties and the situation. Without sounding patronising and judgemental, I would like to reassure you that masturbation is normal. Unfortunately for various reasons, masturbation takes precedence to normal sexual intercourse in a very few people and this can be helped with counselling. The reason for not being able to have arousal and perform despite being able to masturbate suggests either performance anxiety or other psychological issues possibly related to your relationship. Hence it is important that you speak to psychiatrist with your partner. Best wishes.