Hi, welcome
Sorry to hear about this.
In this situation there is only 2 choices imo. The choices are purely yours depending on any level of acceptance you have.
Some partners if a cheating spouse can indeed accept their partner having other sexualising relations. For them it is easier to mentally release them to carry out such activity to keep their family together.
For most partners/spouses their behaviour is unacceptable as to them it breaches trust and causes them to feel inadequate sexually. It damages the love between them forever.
There is no way to make your choices easy nor the challenges you'll face to make the decision to leave. If thats your decision the the best way is to seek a calm conversation with him to tell him directly why based on how you can no longer live in a marriage where its not monogamous. You can pledge to not demonise him to your children and be as civil as possible. Even a friendship could be possible for some people. Then you'd need to be brave and find accommodation and in my experience of separation you'll begin to manage your emotional distress after several weeks. During such time you'd be wise to seek out comfort from friends, your GP and any referrals and sites like beyondblue here where you'll get advise from those that have lived through it.
Finally, its very important that you refuse criticism from your husband and yourself. Based on your post you've done no wrong here.
Its a testing time, you are only responsible for your calmness and desire to work out your future by conversation. If his reactions are verbally violent then you cant control that, you'll have to abandon that approach.
I wish you well
TonyWK
