Maybe there is pain on the road to love, such as when you just got through a tough breakup and feel alone until you find someone who loves and appreciates you for who you are.
I would not, however, equate love with pain and actually believe that those who do so perhaps believe that way because of some trauma they had been through?
Those who derive pleasure from pain, in particular those who derive pleasure from harming others ... have a serious problem that must be resolved before they can interact in a healthy way with themselves or anyone else.