This is a bullshit question that we get a lot from guys: “Is it okay for me to feel [insert any desire or subjective emotion]?” 
In this Q&A, Tucker Max, Dr. Geoffrey Miller, and Nils Parker talk about how whatever you feel and want is cool. Your emotions, what you are feeling, are always valid. If your girlfriend changes, you are not obligated to be attracted to her and those changes. In this case, his girlfriend is trying to shame him into ignoring what he feels. This is ridiculous for many reasons that the guys explain in detail here.
This episode is sponsored by Dude Wipes, the first flushable wipes for men. Check them out on Amazon for free shipping and sales this month.