There's no need to label your sexuality because you're in a relationship, especially if you feel your sexuality is constantly evolving, growing, and changing. Even if you're dating someone new and have defined the relationship, you don't need to define who you're attracted to at large. You can always choose a label later on, once you have a more solid understanding of who you are, or you could go your entire life without ever picking a label — and that is perfectly normal.
As a queer person, my gender identity and sexuality has shifted over time, especially during the course of my relationships with people who have had many different kinds of bodies. Some of those relationships looked straight on the surface; some of them were visibly queer. I've been in relationships with people who presented as cis men, but that didn't make our relationships any less queer.
If you "pass" as straight and cis, you may know that you have inherent privileges in a society that prioritizes heteronormative relationships. But just because you might look straight and cis doesn't mean that you're any less queer than anyone else.
Labels often feel reductive, like they can't adequately express the unique feelings that are behind each relationships. Personally, even though I've been in relationships with people who presented as women, as I do, I don't feel particularly attached to the term lesbian. Physicality feels like such an arbitrary matter to me. We have no control over what bodies we are born into, and very little autonomy in what gender we are raised in from birth. Restricting who you can love and how based off of these inherited qualities feels limiting and even suffocating. I think that when people base who they love off of those qualities, they cut themselves off from being able to experience different kinds of love, connection, and romance.
Labels also give people the feeling that they have to perform certain roles in the bedroom. Classifying oneself as a man or a woman, or as a top or a bottom can create rigid expectations that can be difficult to break out of. Our bodies are capable of feeling immense pleasure if we are willing to explore them. Placing too many labels on the body limits the kinds of eroticism that people might be willing to explore together.
Labels also don't address the change that a person might go through. I personally don't believe that I was always queer. Once upon a time, I did identify as a straight woman. As my world has opened up and I have fallen in love and explored being with many different people, I've realized that label doesn't work for me anymore, but that doesn't mean it didn't function at a certain time. We are constantly evolving, and labels are like skins that can be shed to make room for new growth.
As our understanding of gender and sexuality is constantly evolving and changing, so is our comprehension of our own relationships. But one thing remains certain: no matter who you love, you are always going to be yourself. And while you might one day choose to identify differently than you do now, all that matters is that you are with someone who genuinely loves you for yourself.