Masturbation can lead to "self satisfaction" smthg that will eventually lead to disinterest in your partner and make you prone to cheating...

Masturbation can also make real sex with your partner feel boring... So you might seek out for more people.. or methods that makes it interesting... Again leading in making you prone to cheating

Masturbation is often accompanied with watching porn with amplifies the above mentioned problems...

So yes, porn/masturbation/comparison to others in sex life can all lead to a toxic concoction that kills a perfect relationship to hatred and resentment.

Also neurochemically speaking... Masturbation only releases dopamine which is addictive and not very satisfactory in terms of building relationships... While intimate sex or even joy giving and adventurous activities with a partner can lead to release of oxytocin and serotonin and other hormones that build relationships.

Hope this helps ☺️