Must Read : 8 reasons men lose their erections

1. He’s nervous.
“The pressure of wanting to get hard, stay hard, and satisfy your partner can make it difficult to get hard in the first place,” says Dr. Jane Greer, New York-based marriage and sex therapist and author of What About Me? Stop Selfishness From Ruining Your Relationship. In cases like these, it’s as simple as taking your time and letting his sex drive kick into high gear. Remind him that his penis is beautiful and special.
2. He’s drunk.
Drinking delays reactions and mutes nerves, so his penis won’t get excited the way it’s supposed to. It might make him have trouble achieving orgasm or he might get the dreaded “whiskey dick,” when he just plain can’t get hard. Alcohol is a depressant, and when his penis gets sad, it doesn’t want to get out of bed.
3. He’s overweight.

Read More Here