The concept of unconditional romantic love is somewhat un-natural, it makes sense in a platonic way, sometimes between friends but often family members, because as people sometimes we just need certain things in life that makes us stick a flag in the ground and saying "this is staying just how it is- and nothing will change that". I am fine with certain friends and my family loving me unconditionally and that's a good feeling, that people understand you in such a way that regardless of what you may do or say, whatever actions they may condemn, they'll still know there's a person somewhere in there that is troubled and misguided, but they still love that person.
With romantic love there's much more of an intimate intensity that is ever changing as we grow old and progress/regress. I don't feel comfortable with the idea of a romantic partner being so enamoured that there's nothing I could do wrong, I wouldn't want to feel that way about someone either, it would leave you with this inadequate feeling, somewhat existential, that what does it matter what I do anyway? As people we naturally challenge ourselves, or we should at least, but in a romantic partner we need a lot of different demands from them, and just as important as feeling safe and loved, is feeling challenged. Once you both feel so warm with each other that you "own" each other and nothing will change, you may as well be walking corpses, and I've known people in relationships that felt somewhat trapped in the banality of their rather pointless feelings.
Further on from this is what "unconditional" means in a philosophical sense, is that the intention that you'll love someone no matter what they do? Because it can't be proven as it's an eternal meaning for something we can only say we feel in the present. In this sense I really think people often use the term "unconditional" to ham up their feelings of just saying "love", it's just a way of making it bigger and bolder than love, it's eternal, and this is normally flaky and false.