I will show my code from relevant objects and events and label them and then describe the problem.
//Object: obj_textbox | Event: Draw
//draw textbox
draw_sprite_ext(spr_textbox, 0, x, y,boxscale,boxscale,0,0,255);
//draw text
draw_set_font(fn_textbox);
draw_text_ext(x,y,text[page]...