You can enter into more casual sex relationships with Dorian and Bull. Don't do that to poor Dorian though. You also don't quite have to progress Bull's to a commitment either.
So those options are there.
I love Dorian and his romance, there's a chance I would've made it my main romance, but I can't get myself to play a male character, so misery with Solas it is.
These are casual relationships at first, but I think as soon as you enter the relationship, you can't pursue any other. You can't just get drunk and try with Bull one night, then go on a date with Cullen, they decide you liked Bull enough to go out for drinks with him again, spend one more night, and then ultimately decide you want to be serious with Cullen. You can't kiss Solas in the fade, realize it's the fade, throw a gasket at him for creepily entering your dreams without your consent, avoid him for a while and casually sleep with Josephine, get that warning talk from Leliana, tell her to mind her own business, then get back to Solas when you're not angry with him anymore. Just so many missed opportunities for great stories... Mostly I feel like you're locked into one linear romance that is essentially pre-defined for each character.
My Lavellan will take time. She has loved and lived through heartbreak before. Some of it has caused tension with her clan and some of it has resulted in her closest friendships, but she's not in any hurry to jump into anything after Solas. Again, her sense of duty helps her, but she is affected for some time.
This is very close to how I see it happening for mine as well. She's still on the field with Solas a lot, and I see them eventually becoming friends... Before he bolts, at least.