Many people find that internet porn is like the new toy that is compelling at first but then loses at least some of its allure. Where the laptop is new, this may be a big part of the story.
I suggest next looking at if the masturbation has become an avoidance/addiction. Are you using it to avoid feelings or actions. What would you be feeling or doing if you were not focused on the porn? Hold off for a bit as an experiment and see what gets stirred up.
In general people have a physiologically stronger sexual response to masturbation. Where sex with a partner is a pretty new experience for you time and practice may be key.
Also try scaling back on the masturbation for a week before a date and see what difference that makes.
It may be useful to think of the masturbation and sex with a partner as two separate activities, each with their appeals and complications. But as with many conflicting agendas, the time and energy put into one may take away from the other. Explore if there is porn that works for both you and your partner, that could reduce the dilemma considerably.
I hope that is helpful. Let me know how it goes.
tg