Is it really impossible for a man to change for love?

i’ve heard time and time again that a man won’t change his regular habits just for love/a woman. and that it’s impossible for a woman to change a man. however, i have a friend that has recently told me he loves me, and that he’s willing to quit drugs and whatnot for me. it seems kinda like fantasy to me, but i believe him so far. (it been two weeks and he hasn’t touch a single drink or joint…)