Forcing a spouse to engage in sexual activities against their will is sexual abuse. Sexual abuse is not about love nor is it about enjoying the sex act. Sexual abuse is about one person controlling another in one of the most emotionally damaging acts possible.
Sexual abusers can be male or female although the larger numbers of victims of sex abuse are female and the larger numbers of sex abusers are male. Sex abuse is another form of domestic abuse or violence. Marital rape falls into this definition.
There are many variations in the sex act and almost any sexual experience is acceptable between consenting adults. Sexual experimentation requires trust in each other. Sexual experimentation does not involve forcing a partner to do something that causes them physical injury or mental anguish.
A spouse may want to expand the marital sex to include a third person. All is fine if their husband or wife is in agreement with the arrangement and the third person is a consenting adult. It is sexual abuse if one spouse forces or coerces the other into sexual threesomes.
Anal sex, fetishes, swinging, can all be part of normal and healthy marital sex IF both partners get pleasure from the experience. When one partner is forced or brutalized into participating in any sexual activity, then it’s sexual abuse.
Forcing someone to have sex to “make up” after other forms of domestic violence, or when sick or disabled, is sexual abuse.