You need 38 states to ratify an amendment. Gay marriage was adopted by the voters in 3 states (MD, ME and WA), and by the legislatures in 10 more (CT, VT, RI, NH, MN, HI, NY, DE, MA and CA [passed by the legislature after the courts had invalidated an earlier ban]). So good luck with that.
Another reason I find secession ultimately a better remedy. Sever ties completely with degenerate fag-marriage states.