Suppose for the sake of the argument (and, I think, contrary to fact) that same-sex sexual relationships are on par with opposite-sex ones, except instrumentally vis-à-vis reproduction. I think if one accepts this, then one should not consider sexual orientation to be a significant aspect of one's identity.
If George legitimately loves Patrick, then that should be a significant aspect of George's identity. Likewise, if he legitimately loves Suzy, then he should understand himself in part in terms of that love. But sexual orientation is not love. It is not an interpersonal relationship per se. For instance, heterosexuality and homosexuality are tendencies to develop an attraction only to people satisfying a certain necessary condition (being of the opposite or of the same sex as oneself, respectively), and to be attracted to them in part because they satisfy that condition.
But why should one take a tendency to develop certain attractions to be a significant part of one's identity? Such a tendency is a second-order relational trait. But it is first-order legitimate relationships with other people that, I submit, are what really matters. Of course, if one of these attractions is to morally illegitimate relationships, then it may matter for one's moral development that one does or does not have that attraction. But I was assuming, for the sake of the argument, that both kinds of relationships are legitimate.
However, one might think that if one's sexual orientation is unjustly discriminated against, then it makes sense to identify with it, out of solidarity with other people who share that orientation. If so, then there is an extrinsic reason to identify with a sexual orientation in the face of discrimination. That said, I am not completely sure that unjust discriminators should be allowed to dictate what we identify ourselves with (I have some Danish ancestry, which I hardly identify with; if there were discrimination against Danes, should I start identifying with it?). Still, I feel the force of the idea. And, if this response to my argument works, then it makes sense for non-heterosexuals to identify with their sexual orientation to the extent that they are the subject of unjust discrimination.