I'm not sure about Deida's sexual advice. I tried following it for a while, but if what he says is meaningful, I found it too hard to follow. Now I'm doubting whether it was. I continue to masturbate whenever I don't have a woman, and it doesn't seem to do me harm. On the other hand, stressing myself and feeling guilty about masturbating really did.
I've never had the problem, so I don't know how to make your sex last longer, but in general perhaps you need to relax more. When I feel myself about to come when I don't want to, I take some deep breaths. Meditation is good, though meditation is something you learn over a long time. Having a quiet mind is like weight loss or muscle building, you can't look for a quick fix, it's steady effort over a period of years.
Another trick you could try: bunch your fists up as hard as you can. This is supposed to get blood flowing away from your penis, removing the pressure. It works for me, though if she sees it she might wonder what's going on
If all else fails it's OK to tell her you want to stop because you don't feel like coming yet. Then go down and pleasure her with your mouth until you're ready to go again, OK?