Here's a suggestion....take a HUGE dildo and shove it in your butt. It will prob hurt like hell at first and maybe even bleed, but you will eventually (maybe after 5-6 attempts) figure out how to get something over 4 inches in your ass. When you figure it out on yourself, then advise your girl how to do it.
So in other words, do it to yourself then to it to her....100$ says you will be over your anal obession.
Boys and their obession with ass.....it's so gay!