So using your "logic", a person who is inherently sexually attracted only to somebody of the same gender as themselves, but only engages in sexual activity with people of the opposite sex (out of a desire for social acceptance among his/her peer group), is fully heterosexual and not gay.
First, it's not "my" logic, and it doesn't need quotes. It's plain and simple logic. Unless you can argue successfully that it isn't logic, then stop pretending otherwise.
Second, yes, if you only have romantic and/or sexual encounters with people of the opposite sex, you are heterosexual REGARDLESS of who you find more attractive.
It's LOGICAL because it can be applied across the board.
For example, if I'm only attracted to blondes but only have romantic and/or sexual encounters with only brunettes, then I would be someone who favored those encounters with brunettes, REGARDLESS of the fact that I'm only attracted to blondes.
Bottom line: You can choose to be with people who aren't your preference if you want, and people do it all the time (if they didn't, everyone would only be with someone they find incredibly attractive, and we all know that isn't true).