I'm trying to think of an unhealthy relationship in DAI... and I'm not really thinking of one. There are relationships with unhealthy people, but the relationships themselves tend to be healthy, and help the person involved.
The worst is probably Blackwall, since it's built on a deceit. This is iffy- the Blackwall we meet is the only one we've ever known, and the personality and interest are genuine as well- and as far as flawed relationships go, it doesn't even register. Good man with bad past hides bad past for good woman. More at eleven.
Solas is probably the worst person all things considered- the least socially adapted- but at the same time, the romance is one of the most humanizing (or elfenizing) things about it- it breaks through his internal bigotries, that people aren't people, and he approaches it seriously and considerately, upto the point where he WON'T exploit the ignorance of his true identity. Solas is a mess, but the relationship isn't.
Sera's another person where the relationship is better than the person. Sera's chaotic and immature, with some touchy points- but the relationship is a stabilizing point for her. Hes, people are free to criticize her break-off point following the Temple of Mythal, a clearly stressful and disturbing point for her- but that's an unhealthy or even harmful relationship. It certainly helps Sera stabilize in ways she hadn't before.
Cullen is practically a textbook for a good relationship helping someone through a troubled time. Cullen's not healthy- he is addicted- but the relationship ackowledges that, and chooses to deal with that as a couple despite knowing the difficulties. That burden of sharing hardship is very, very healthy- freely given, not exploited, and truly cherished.
Cassandra's a boss. A little tacky, maybe, but morally impeccable, unless your morals include demands you be number one in all things forever. Which really wouldn't be healthy.
Josephine is another good one. Mature, reasonable adults handle matters in a fanciful but mature, Disney way.
So DAI? Pretty healthy relationships all around.
Now, DA2...
DA2's friendship romances were pretty risky all around, because they typically entailed indulging flawed or even self-destructive behaviors. Some more than others- Fenris's PTSD could be helped in different ways- but the other three typically entailed avoiding self-responsibility and addressing character flaws. Merrill is a bit iffy, depending on where you stand with her position (though you encourage her obsession), but Isabella and Anders? Friendship Isabella is absolutely encouraging selfishness, greed, and irresponsiblity while Rivalry is putting a boot (and maybe some other things) up her ass to adopt basic morality. While Anders friendmance is absolutely enabling and encouraging increasingly sociopathic obsession.
DA2 had some unhealthy relationships.
As for DAO...
Eh, Leliana wasn't unhealthy per see since it was a basic love, Morrigan was questionable since it started bad but became something healthier, Alistair was a guy whose romance didn't really make any of his flaws worse and accentuated his virtues, and Zevran... eh, if you wanted conventional and healthy, you wouldn't have spared him in the first place.