Don't base your sexual expectations off porno's.

Best piece of advice that can be given.

For a more direct answer to your question, cum changes from guy to guy, and (I believe anyway) is based very much upon your diet, and length of time from your last ejaculation.

For lasting longer, you'll find it is mostly psychological as opposed to physiological. The more anxious you are over sexual performance the worse you are likely to be.

Masturbation technique can help you somewhat, making yourself pause before bringing yourself to orgasm then restarting.

But the main thing is to stop worrying.

If you're in bed and the only thing running through your head is not to cum, you'll find thats probably the only thinkg that WILL happen.

Relax, think about pleasuring your partner, and enjoying everything they do to you.

Final piece of advice is to consider positions. Most guys have problems lasting whilst in missionary, but perform much better lay down with the woman on top.

Good luck