I think you're describing a pansexual. But maybe I got it twistid.It has nothing to do with liking somebody for years at a time. It's just an attraction to whoever you feel close with ( male or female), But bisexuals tend to have a preference though.
I believe bisexuals go though waves, but can still settle. And that thread that they can't be committed partners was sad, because bisexuals can be decisive and sure if married. Bisexuality is so deep and personal many in LGBT community don't think it exist. And even larger members of heterexuals don't believe in it.