I've seen a lot of kiteman x ivy vs harley x ivy arguments recently. Neither ship is perfect but people seem to think that kiteman x ivy is. Even the producers have said it's not, no relationship is. They wrote the characters well with emotional depths. The relationship is realistic.
But if you look at the psychology of it, it's not actually that healthy. Ivy avoids meaningful relationships through a fear of getting hurt. Due to kitemans parents treating him the way they do, he has a pathological need for everyone to like him so is overly nice to everyone.
This means he's a safe partner as he won't do anything to hurt her. He unconditionally and instantly loves anyone who treats him with the slightest respect and is therefore a safe choice for ivy. She's with him because there's no risk. He's safe. She likes the idea of him because she feels like she's unworthy of love. Ivy doesn't think that anybody else would love her and stay, because nobody ever has. There's a reason she turned down his proposal so many times. She loves the relationship not him.
This is also why she turned harley down. She loved the idea of being with her, you can tell that, but she is too scared that Harley will break her heart. Harley is impulsive and has extreme highs and lows in all relationships. Ivy has constantly feared that Harley will abandon her as it is. She said as much last season. She finds it hard enough relying on harley being there as a friend. Being in a relationship with her would mean being even more vulnerable. She would have more to loose and ivy simply cannot deal with the possibility of being abandoned by another person she loves.
So, she settles for the safe option. The one who won't leave because he'll do anything to feel wanted himself. He's scared she'll leave too so he does everything he can to keep her happy. They both appear happy from a distance and they are. But happiness/security and love are different things. We love the idea of them and some people (like ivy) can often mistake these for love.
In the long run this is not healthy for either of them. I'm not saying ivy x harley are healthy either but they would be together because of love, not as an emotional blanket. This could be messy but it's also a healthy step for developing both characters emotional development.