I thought that it was only for lovers and mothers to use..... would there be a specific diminutive of her name mostly reserved for a boyfriend/lover/husband?
No, Insomnia is right.
Btw, to be honest "Paulinka" sounds a bit childish (at least to me), usually only my aunts call me like this lol (except for the one that calls me "Paula"). My female cousins, who are younger than me, call me "Pauliś" (in case you would like to use something even more diminutive and familiar than "Paulinka") ;)
usually only my aunts call me like this lol
And my uncles (sorry, I forgot about them lol).