Sesquisexual

A sexual orientation where a person is primarily heterosexual but occasionally experiences or expresses bisexual tendencies. This person feels attracted to people of different genders in "one and a half" instances, with the heterosexual orientation being dominant but with occasional bisexual interests emerging.

George: "So, I hooked up with a guy last night. It was pretty great!"
Jerry: "Wait, I thought you were into girls!"
George: "I am! But, you know, sometimes a guy just catches my eye."
Jerry: "Sounds like you might be sesquisexual!"