Well I romanced Morrigan in DA:O and she did leave at first, but then I went through the eluvian with her and they lived as a happy family together with their son for quite awhile, before my Warden had to leave to search for a cure to The Calling. So technically they weren't apart at all really.
Then in DA:2 I had my female Hawke romance Merril, and I'm pretty sure it's the same for male Hawke's as well in this, but if you ask Hawke about "friends and family" like most people do then she'll (he'll) tell you that she told Merril to keep helping elves in need instead of following her.... or him. So they are together for a bit, but in this regard Hawke will "leave" every single romance in some way or another so don't complain about it.
As for this game, DA:I, I romanced Josie, so that worked out quite nicely for me lol But in all honesty, the Solas romance I never expected to actually follow through, as soon as I heard you had to be a female elf in order to have the option I knew it wouldn't be a complete "final" romance. Not sure why, I just had a feeling that if it was THAT specific then it would play a larger role in the overall story and end up not working out 