Thank you for explaining that! So, sometimes people build up what masturbation or sex feels like in a way that just isn't realistic. Yes, sometimes those things can feel really, really good. But they can also feel underwhelming, or just plain bad. And how they feel varies not only from person to person, but for an individual person throughout their life. It sounds like you can and do feel pleasure from some kinds of masturbation, so there's nothing to indicate that partnered sex wouldn't be something you could enjoy.
Too, lots of people don't feel a ton pleasure inserting their fingers into their vaginal canal, since as a whole it's not as sensitive as some other parts of the genitals (you can read more about that here: With Pleasure: A View of Whole Sexual Anatomy for Every BodyWith Pleasure: A View of Whole Sexual Anatomy for Every Body
When you're masturbating, are you aroused? And is your brain engaged in what's going on, or is it more that your body is trying to masturbate while you're brain is focused on other things?