General masturbation/sex advice

Hey guys, I’m 18M, I’ve been masturbating regularly(but not daily) since I was around 14-15 and I still feel ashamed every time I do it. I feel as if someone is watching me every time and it feels unnatural. Anyways, I am at a point where I am going to try to start dating and if I ever hookup or date, I just want to know what I should expect, how do you even plan to have sex or is it more of a natural thing, and how can I not feel ashamed while having sex/masturbating. Also I feel like the material I get off to is weird, like I will see a girl on instagram or something and then that becomes sort of my source for the whole week, which feels even worse doing than actually masturbating. Anyways I just want to not feel bad and I want to make sure I am fully prepared in case I date or something pops up since I am a maturing adult at this point.