My manager says she wont investigate my sexual harassment claim.

I've been getting sexually harassed by a co-worker for awhile now, we've worked together for 7+ years but recently after his divorce he's started making sexual remakes and statements about me, I talked to my manager about this and she says there's nothing she can do because it'll be a he says she says situation and he would just get our union involved. I feel all alone and I cant just up and quit.