Also, there is something called age of consent which means it can be against the law to have sex below a certain age, which varies from place to place.
If you keep up your rough sex play, you're apt to continually aggravate it.
I even think it's unusual that all of your girlfriends have admitted they masturbate, because in my experience, a large share of women either don't masturbate or don't admit it.
From what you describe, the problem is probably not your partner's size but his rough penetration.
Is there something wrong with me?
You should enjoy them and be glad you're having them frequently.
These alternate identities are commonly known as alters or dissociated parts.
Could my partner's large size have anything to do with it?
Perhaps your mom knows best?
If there is a person his age who does not masturbate, I suspect he would be asexual and very confused and clumsy in the bedroom.
Work at finding a regular sex partner.
By age 16, not very many do.