You mean like doggie style or missionary? Yeah, me neither. But you and I orient ourselves by our sexuality to some degree every single day ~ when we use the term "Mrs" or when we wear our wedding bands or when refer to our husbands. You just do it so cavalierly as part of heterosexual privilage you don't even recognize it, of course. Your straight sexuality is a very overt part of your life as a wife and mother of children.
Do you realize that by identifying as a heterosexual that you use the definition you posted previously but instead of same sex it is opposite sex? It's the SAME definition besides that one word.
I don't identify myself by my sexual actions. Before I made my "sexual debut" (yes I stole that and I love it) I knew I was straight. I liked boys and only boys. Girls were only my friends. Even after I had been sexually active, there were times I wasn't having sex and I still would identify as being straight.