I didn't find DA:I's ninjamancing to be that bad - mostly because all the romance enabling options have a big pink and red shiny heart icon which screams FLIRT every time you hover over it. As well as that, DA:I tends to also change the look of the dialogue wheel when you make a really massive choice.
I think I've only actually ever flirted with Solas, Sera, and Harding for that reason.
Part of the issue with Solas, and to an extent the ninjamance of Blackwall, is that it takes more time to dump them and move to someone else, but it is possible to start with a couple of people. Even if things get more committed with someone like Dorian you can hurt him by keeping it casual. But it's still a casual relationship. Still if you want three and foursomes, not in this one. But I find the romances mostly better overall.
Some of them will also tell you to go dump so and so before they'll even be open to anything. Like Sera.
I like hers if you're romancing Solas. Something like 'If elfy's not doing it for you anymore, tell him first. I won't be anyone's second'. 
That line is half the reason I flirt with Sera. Also, because she's Sera.
Everytime I play ME1 I have to avoid talking to him after a certain point until post-Virmire and I'm locked in with Liara.
And, because it needs to be said again:
STOP. FLIRTING. WITH. JACOB. SHEPARD.
I'm now working through my third full playthrough of Mass Effect (it's what I'm using to kill time between now and DLC) and because of this, as a rule, I just don't ever talk to Jacob.
I don't say hi. I don't do his damn loyalty quest. When he offers to climb through the vents on the suicide mission, I just let him do it and have him die. No major loss.
After playing through ME1 though, DA:O's ninjamancing seems a walk in the park. At least in DA:O you aren't 'locked in' and can at least be presented with jealousy dialogue. In fact, if you play your cards right it's not an issue at all. Hell, I think with my first playthrough of DA:O I was technically romancing both Zevran and Alistair (a sort-of-on-purpose-accident, I struggle to not flirt back with Zev, regardless of roleplaying, ahaha). I am not a very good person in game, it seems.