He lasts too long.
It's called retarded ejaculation: He's not able to ejaculate when he wants to, despite intense and prolonged thrusting or oral sex. Initially, men tend to think God's just handed down a very special present. But after the thrill wears off, it becomes frustrating and often painful. Most men also quickly figure out it has the opposite effect on women than he first thought; it cuases concern rather than pleasure.
- Is he on anti-depressants? If so, that's probably the culprit for tardy orgasms. If he's tired or under lots of pressure and this is the first time you're noticing this issue, his exhaustion is probably responsible. Age also effects the pace of ejaculation.
- The first step, as usual, is to get a full medical exam. Prostate problems are sometimes responsible so you must get it checked.
- Is he too embarrassed to ask for something he needs to tip him over into orgasm (a finger inserted in the anus, for example)? Make it clear you're happy to indulge any reasonable request.
- Can he masturbate himself to orgasm? If he can, it's probably not a medically based problem. He may be focusing too much on your pleasure, afraid to let go (perhaps because of a previous pregnancy scare or infidelity) -- or he may have control or power issues in the relationship (he's angry and feels a need to “withhold”).
- Desensitization techniques are effective to get him used to ejaculating with you, rather than just solo. He starts by masturbating in another room, while you're in the next room with the door open. Next, he masturbates while you stand at the opposite side of the same room, but facing the other way. Finally, he works his way closer and closer until he's able to bring himself to orgasm while you lie beside him. From there on, it's baby steps till he's inside, happily thrusting away and problem sorted!