Surprise him by your maturity, sense of security, and independence.

If he notices blonde girls specifically to exploit your vulnerability, he might stop once he sees that you are not vulnerable anymore. If there is no vulnerability, there is nothing to exploit. You cannot hurt someone with good ammunition. Do not let him get a rise of you. Volunteer appreciation of other girls physical beauty. You are a big girl and you can handle it.

Another tactical trick is to start noticing men. I was not exactly clear why you do not. If you cannot, then never mind, it is your immutable feature. You cannot adjust factory settings. I was incorrect yesterday saying that I never do. Just very rarely. Yesterday in the three hour movie I noticed one pleasant male face and several female ones. That is typical of me. In East Asian people, I only appreciate the beauty of select female faces and neever male ones. I am perfectly straight, btw. But whatever, if you are like me, there is little to be done about it, but if you are not like me, if you notice cute guys but hide it, then STOP! For goodness sake, stop. Let it be known that you do. Let him deal with it.let him have a taste of his own medicine. This would restore the balance of power between the two of you.