If Trump wants to be able to defy Ryan and McConnell and set his own agenda — either because he is serious about the less conservative parts of his campaign platform or he simply hates ceding power to others — he needs someone else he can work with on Capitol Hill. That will require developing a working relationship with Democrats. By being able to work both sides of the aisle and build situation-specific coalitions, Trump would have a much more powerful presidency than if he pursued a narrow Republican-only strategy. And I doubt he'll get in much trouble with Republican voters for it.
No, Trump does not have a good relationship with Democrats. A relationship implies a give and take between both sides. Trump does not have much give. It is only take with him. Any perceived relationship is based on how he can benefit. In addition, Trump has not been trustworthy, another important aspect of a good relationship.
Trump does not have a good relationship with Democrats. But, then again, why should he? He is a republican. He won the election. It's up to democrats to work with Trump. Want it your way? Then win elections. Now is the time for Trump to keep a backbone and do what he said he would.
The Democrats are too busy crying after the election in order to have a good relationship with Trump. They are too busy interrupting their own musicals and complaining about Pence to work with Trump. Trump is more of a centrist than people realize, and the democrats would be surprised if they actually tried to work with him.