A romantic relationship develops linearly beginning with physical properties; the appearance of characters is immediately apparent. Physical attraction, ambivalence, or repulsion may be instantly established to aide or hinder future relational growth. Over time more depth will be revealed about less superficial character traits by observing what sort of hard choices the characters make when faced with conflicts. These exhibited character traits will either be favorable, enhancing the relationship, or they will be disfavorable, posing obstacles to the relationship. As with any conflict, a romantic conflict is one where the character is faced with a decision that must be made, and that will have lasting consequences of some type regardless of which way the choice is made. These hard choices both arise from, and expose and reinforce contradictions that are inherent in the character. We are unsure what the character will do, because he is kind, yet insensitive, or because she is eloquent yet self-conscious.
In a romantic relationship, these contradictions often lead to an emotional desire to care for the object of affection vs. an intellectual knowledge of sacrifices that must be made to do so. Romantic emotions are terribly strong: Not mere desire, but longing! Not mere pain, but torture! Not mere loss, but desolation! Strong emotions require desperate situations and lead to extreme choices.
This gradual disclosure of character often runs in parallel with an establishment of growing friendship, trust, preference, and care between the romantically involved characters as symptoms of their relationship. These emotional ties are what we see being endangered by the hard choices the characters are faced with.
Romance is contingent on developed characters, without which the key feature of continuing mutual discovery by the romantically related characters can not take place. Why is an element of mutual discovery so important? After all, characters may be defined to be in a romantic relationship as an aspect of setting. The problem is, without incremental disclosure the growth of this relationship can not be shown and empathy between the reader and the characters can not be established. In service of the axiom: "Give me me; I want to live more!" the reader needs to be brought to know the characters as the characters are brought to know each other. In The Last Samurai we fall in love with Taka along with Algren. In contrast, consider a situation in which a male character is introduced who immediately swears to protect a female character, then subsequently fails to do so. This is not a dramatic failure in a romantic relationship; we have not yet had time to establish such a relationship. Rather it is a demonstration of the new male character's general unreliability. It is character development that may be necessary to establish a future romantic relationship where one does not yet exist.
In order for the relationship to grow as described, the setting must offer sufficient opportunities for the romantic characters to be together - otherwise they can not learn about each other. However, the setting must also allow sufficient scope for keeping them apart so that they may reflect on the pain of separation.
The success or failure of a romantic relationship must not be a logical necessity. Whereas suspense is driven by delaying the inevitable, tension comes from the unknown. We may anticipate from genre conventions that the relation ship will (or will not) turn out well, but the truth value of the actual result must be ambiguous until we reach it at the climax - failure, success, and perhaps compromise must all be logically possible, even if some particular outcome is unlikely. In Rebecca, Du Maurier downplays the romance element significantly compared to her treatment of it in Frenchman's Creek. And yet the ambiguity in Rebecca is much more emotionally powerful than the predictably escalating lustful encounters of Frenchman's Creek. Frenchman's Creek is an adventure of piratical one-night-stands that makes your blood race. Rebecca is a rollercoaster of romance that makes your soul cry for solace.
The status of a romantic relationship is thrown into uncertainty by the choices the characters themselves make. There is almost no romantic tension in Shakespeare in Love. In spite of the fact that Colin Firth's character ultimately prevails in separating them, the romance between Will and Viola is clearly a success. Comparatively, the anime School Rumble is driven by quite a lot of real romantic tension, in spite of being a parody of romantic comedy - because the characters themselves are always screwing up and saying or doing the wrong thing. This is exactly the case in the comparison of Rebecca and Frenchman's Creek. In Rebecca the characters hide their feelings out of fear, and continually endanger their relationship with their own actions. In Frenchman's Creek the characters are ultimately committed to their fling - the conflict is that of adversity; that the romance is healthy is never questioned.
Romantic tension is increased when a character makes the wrong choice; romantic tension is released when a character makes the right choice. A "right choice" in this context is a self-sacrificing one made in favor of the object of affection. This path of increase and release of tension must eventually be followed. However, suspense may be injected by delaying the inevitable through misunderstanding, angst, and circumstances.
Eventually, a point will be reached where it is unsatisfactory to continue the wave-like progression of tension and release and the delaying tactics of suspension. The characters have been sufficiently developed and their relationship adequately explored. It is time for a climax to escort the romance to its fated final resting place. The timing of the climax is important. Too soon and it will seem shallow - without enough development we don't know the characters well enough to empathize with them, and there will not have been enough adversity for it to be meaningfull. Too late and it will seem superficial - our attention will have been distracted by the neverending tide of emotional gimmickry which is only now being brought finally to an end because it has become boring. If the romance is a feature of a larger work, once resolved its status should not further be brought into question. If the romance is the focus of the work, once resolved, end the work.