CDs can sell too fast which is why I included the option to delay. If Robin won't hang out with him, that means they're in a bad place in their relationship. Have you seen the Rooftop scene? It's one of the longest cutscenes in the game so I think you'd notice. If not, see if Emmitt has something to say. There's a dialogue that progresses Dallas' romance. Sometimes chars you aren't dating get ignored so maybe you didn't go through Emmitt's dialogues this time?
There is one thing you can do that cancels a romance route, and that is not leaving Sterling's apartment with Dallas when presented with the option.