In: Psychology
There is no such thing as normal and perverted sex
If the sex life is comfortable, enjoyable and working for the partners then it would be considered normal no matter what others are doing
If the sex life is pushing one partner out of their comfort zone, boundaries, feels uncomfortable, unnatural and demanding too it will not be working for both of them then we might call it to be not normal not because its working for others but because its not working for the partners as both are not equally happy and comfortable with their sex life.
A lot of domains related to sex like BDSM might be normal for someone and might be perverted for someone else. It is all about what makes you happy and enjoy sex with your partner. If BDSM is you and your partners fantasy and you love the sex then it is completely fine and normal but if it makes one comfortable and forced to do it for the partner it might be perverted
It is all about the sexual relationship and an understanding between the partners what is normal for them and what seems beyond boundaries or what do they define as perversion