Beliefs shape the way we feel. There’s no biological reason to feel lonely after masturbation. That’s all pseudoscience bollocks. Female orgasms cause a peak of neural activation, if anything, you should feel more active and hungry to go face the world. But the point is that this changes or differences that are usually quoted by charlatans from neurological studies, while significant, are so tiny as to not be an actual factor at an individual level.

Humans are also bad at correctly discerning causation and correlation, specially within their own emotional experience. Thus why therapy works, it’s a third party that can more objectively call out your contradictions and point out causes.

Now I would gather you believe that masturbation is something awful lonely people do and that’s why you feel lonely when you masturbate. This doesn’t mean there’s anything inherently wrong with you. However, most people ignore that most of our worldviews, and beliefs we take for granted are actually cemented in childhood experiences, not always traumatic. But they do build the foundations op our personalities.