I think with your dates it might not be as bad (crowd-wise) as people think. Things are really getting hyped -up on these boards, but the general population has no clue about SW:GE.
1. Most people plan their vacations 6-8 months in advance. If Disney only gives a few months notice about the opening, I would say more families will be planning for trips in early 2020 to enjoy SW-GE than those who will make it there in December. It will be die-hard fans and vloggers who will be there right at opening, not your average family. But that's just a guess!
2. Most people plan around kids / work holidays. My bet is that the week between Christmas and New Years will be unbearable, as will Spring Break season. It will be busier than usually when you go, but not a nuthouse. Most people cannot get off work or pull kids out of school at the drop of a hat. They need to plan well in advance. I think the nuthouse-
in-every-park scenario will start a month or two
after opening...once word of mouth and social media have done their job. And then, my prediction is that the big crowds are not going to end until a year after the 50th Anniversary in 2021.
All that to say, if it were me I wouldn't change dates. I'd make a plan, rope drop to avoid crowds, enjoy resort hopping and the pool to relax, and make some great ADR's. I'd say your bf will love it! Take a deep breath and happy planning...