If your hair is thick, then growing it long would help it straighten it out naturally. Very think hair, when short does become course, especially when you have just washed it.

Also, an element of suprise will always help. It seems like your boyfriend may be a little shy in expressing his fetish to you fully, not knowing how exactly you may react (trust me, I have been there myself!!!). So, as and when you learn new tricks, if you try it out with him more subtly, seeing his reaction to it could be a great turn on for you as much as it would be for him. Also, quitely growing your hair longer without discussing it with him will also be a pleasent suprise to him. After a month or so, you will see him reacting "Hey sweetie, you have'nt cut your hair!!! It's seems to be growing nice and long". Any you will have him on his knees begging you to grow it even longer!!!!

Have fun and enjoy