Unfortunately there’s no shortcuts on this. Welcome to the challenge of learning self-discipline. This is one of the reasons why I think denial is a wonderfully positive kink. You’re learning to deny yourself short term pleasure in return for a longer term reward. That’s a huge life lesson, let me tell you now. It’s probably the cornerstone of most successful people.
The Marshmallow Test
Mastering denial has the potential to truly change your life. The ability to delay gratification is so important, and that was best shown by the work of Walter Mischel who did the famous test with young kids, offering them one marshmallow now or two if they sat and waited for 15 or 20 minutes and didn’t eat the first one. Watch the video below for a nice summary of what they saw when they came to look at the SAT scores of those kids and all other kinds of indicators later in life! (Also a fascinating summary on lots of self-control psychology).
The other major point to factor in is that you’re still learning, stop expecting to run before you can walk. You will cum sometimes as you practise this, stop feeling guilty about it and determine to do better next time and get back to enjoyng it!
Also, look up ruined orgasms on this blog as that’s the other answer, learning to ruin the orgasms when you do go over soon helps you deny yourself longer and harder.