Would you date/have sex with a step brother or sister in this cases?

If you two knew eachother when your divorced parent decided to have a bf/gf again and they had a daughter or son, and she/he is into you, would you step forward and have a relationship with them? Or, if you are already in a relationship with someone and your parents got together would you stop seeing each other as a couple?

For me, if I truly love her I would stay with her because it was a decision of our parents not ours. Sex? I am not so sure I would keep that up if I don't love her deeply. It would get complicated if we fought yet still had to see eachother.
Would you date/have sex with a step brother or sister in this cases?
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