Language help

I am an American and am in love with a lovely man from Arnhem. He has lived here in the US for over 10 years and speaks English wonderfully. He is planning on proposing. Regardless of his English speaking ability, I am determined to learn Dutch. His family is all still in the NL and speak Dutch. I have had some little conversations through text with his mother, but I rely heavily on Google translate (which is fine, for now). Reading some of the posts here, I am picking up on some words that I have learned from Duolingo. I'm struggling with trying to make sentences and put words together more naturally. Do any of you have any suggestions for how to learn Dutch? Any websites or books that might help?