Medically/scientifically, I have no idea. I probably should but it wasn’t covered in my class.
I do know that if my boyfriend is turned on too often without that release, either through sex or masturbation, he experiences a lot of pain from buildup.
I also know that if we’ve just had a night of rough sex, he is sore the next day. (supporting @Neizvestnaya ‘s comment).
As far as sex drive afterwards, I think it depends on the person. Some people can be super horny and ready to go only a couple of hours after orgasm, others need to recover for a day or so. And when I say orgasm, I include sex with a person or just masturbation. It also depends a bit on the penis. Specifically: circumcised or not. If uncircumcised, some guys are a little more sensitive to the tugging because of that foreskin. Increasing the effect of rough gestures.
Regarding relationships, I agree with @Coloma.
If you actively enjoy masturbation and sex, a comfortable relationship with your partner should involve discussing it. I don’t see anything wrong with people in relationships masturbating as long as it is addressed, because it can lessen desire and if the partner doesn’t know what’s going on, it can be painful and frustrating.
I was not always of that opinion regarding masturbation. Talking about it more is really the only thing that made me realize it isn’t a problem