I ask what he likes out of curiosity, but I am going to do what I want with my hair. Especially since it is my time, energy, and money spent going to a salon/doing it myself. I also would think it was kind of rude if he told me my hair looked "weird" unless I asked for his opinion, but maybe that is me.
Maybe you can stress other benefits to him. My boyfriend likes that I no longer cringe every time he touches my hair (flat ironing took to much time for someone to go touching it and my curly hair had to have so much gel it felt disgusting), I'm much more easy going (rain, snow, pools, even humidity to an extent, etc. are no longer my enemies), it takes me significantly less time to get ready, and I'm happier