I can see there might be two issues here. One is the cognitive issue, which is your beliefs around this issue. Can you believe, in your head at least, that there is no need to define your sexuality? It can change or be in flux. You might be flexible sexually.

The second issue is your emotions and unconscious attitudes. It is here, it seems, that you struggle... you can't seem to settle on a conscious attitude that is acceptable, because immediately anxious thoughts of distress start up. If you are straight, you worry that you really are attracted to women. If you imagine a relationship with a woman, you aren't sure what you feel so you suspect you are straight. You have thoughts like "I want to be gay" but then you worry you are fooling yourself.

You might need to explore the deeper issues around this in therapy. There may be some feelings left over from your formative years that are influencing you unconsciously. And you may have OCD, and you may need to get some help in separating OCD thoughts from your core identity.