I am a 19 year old male who has recently become sexually active. So far, I am able to remain hard and climax without difficulty as long as my partner and I stick to oral sex. But when I am preparing to penetrate my partner, I immediately get soft upon contact. The condom goes on fine and I am very aroused and excited about the prospect of penetration, but I can't seem to stay hard when the time comes. What's going on?? note: there has been one occasion that penetration was possible until climax, but I was intoxicated