I will not make the claim that unconditional love doesn't exist. This is not to refute the existence of the vast reservoirs of possibilities for the expression and our perception of all things that bask in the pure potential to appear to us as amazing, holy even. However, I will claim that you're using the term incorrectly.
When you say, "I love you unconditionally," even the syntax betrays you. You are using love here as an active verb, one with a direct object, and establishing yourself as the agent in the exchange. What's problematic here is that, according to Buddhist philosophy, any action is a changing thing. And any changing thing is a caused thing. Being a caused thing means that it is the result of causes and conditions, and is therefore necessarily conditional.
Allow me to paraphrase the Shakyamuni Buddha's Four Arya Truths:
1. We suffer.
2. There are causes for our suffering.
3. We don't have to suffer.
4. There are causes for our not suffering.
Ultimately, we suffer from not understanding the true nature of things, when we apply our corrupt theories to our experiences. It's so easy to do, and we're taught to do it nonstop. We teach others to do it nonstop. We think our experiences of the phenomenal world are self-existently true, and that our assessments of each moment are accurate. "I'm in love, we're soul mates" can be just as ignorantly experienced as "you broke my heart." Wisdom, which is cultivated through mediation and supported by cultivating deep concentration and an ethical lifestyle, reveals to you that each experience is not inherently the way the mind perceiving it claims. Your perception of the universe in this moment--whether it's delight in a sweet Valentine's card, annoyance at a pop-up advertisement, weariness of the godawful cold weather, or wonder at a GIF of a dunking contest--is a product of your mental habits, caused primarily by the previous moment. And since we cannot change the previous moment, the only opportunity we have to affect the next ones is in the present.
Wisdom would not have you, somebody who enjoys love, passive in your participation with love. Wisdom knows the third Arya Truth, that you don't have to keep randomly pulling the loves-me-not flower petals. Wisdom urges you to act on the fourth Arya Truth, that you can create the causes for experiencing your love life vibrantly and positively.
Conditional love can be, but is not inherently awful. The common construction of the idea of unconditional love conjures its supposed opposite, a binary opt-in, opt-out kind of slot machine love, whose output is the function of some algorithm in a system of exchange that is rigged against you. The so-called lover wields so-called love only on certain terms; it's sort of like hostage negotiation, and the hostages are intimacy, affection, touch, social standing, and certainly power. The question this variety of conditional love asks is merely loves me or loves-me-not, and it's not very sophisticated.
Let's instead consider a conditional love that is more communicative and adaptive. Love that is active, which is to say changing, which is to say caused, and adapts to meet whatever conditions arise. This is the practice of engaging with your Loved One, and customizing your practice to meet the new conditions that life presents you. Mind you, the sophisticated question this variety of conditional love asks is, what is the best way that I can actively love given the circumstances? What do these conditions ask of me?
Do you realize how amazing the implications of this could be? Since the experience of love is a caused thing, we can create the causes to experience things as love. Since the act of love is caused, we can act to cultivate a practice that allows the feeling to thrive, to radiate through our thoughts and words and deeds, to seep into our daily life more and more. Perceiving love as conditional opens us up to more sophisticated and less binary interaction with love.
So don't stop thinking about unconditional love. But try, when accessing it, to drop the unhelpful "unconditional" and participate actively in the practice of loving, responding to the conditions, and optimizing and growing in your capacity to serve others, to delight in huge wonders of the universe, and to connect with one another.