Romance Writing Problem: How to Keep Characters Apart

The bodyguard and guardee is one of the

most romantically charged tropes.

In children's fantasy, the writer often has to figure out a way to get rid of the parents. It is so much easier for children to get into wardrobes, takes trips with Greek gods and goddesses and find themselves in the care of witches and warlocks if hovering parents aren't around.

In romance, the writer often has a to figure out a way to keep the romantic leads apart (even when they are working together) in order to build romantic tension. Here are some common approaches:

The Job
The romantic leads are captain and subordinate, boss and assistant, teacher and student. These roles are surprisingly effective since even when no legal or official rules separate the romantic leads, the characters will feel social pressure to stay apart, especially if either character is ambitious.

Class & Age
Class actually has more impact than most romance writers (and modern Westerners) will admit. People still tend to date and marry within their social class. Family and personal expectations about lifestyle still hold sway.

However, this reason is rarely directly addressed in contemporary romance. Social expectations regarding age, on the other hand, still hold sway. The May-December relationship is a classic trope.

Historical Expectations
Historical expectations--courtship should take this form--are the most effective, largely because they belong in the under-the-water part of Freud's superego. That is, they are powerful precisely because they are unstated. Good contemporarily-written historical romances will try to do what Austen and Bronte did unconsciously: not explain themselves.

Past Trauma/Pain
This form of separation--the leads can't get together since they are both so haunted by past misery--brings the violence trope into play. It is inherently problematic. It can be effectively done, but if too extreme, the reader might doubt whether the relationship will last past the couple's meeting followed by separation (due to unresolved personal issues) followed by reconciliation. Then what?

Past Bad Relationship
One or both members of the couple has trouble trusting again. This is probably the most common reason presented in romances, and it can be effectively written. As with the past trauma/pain reason (see above), it can leave the reader wondering, "Can the relationship survive so much angst?"

Enemies
Jane Austen! Yup, Darcy and Elizabeth are the most classic example of romantic leads who think that they dislike each other when they really don't. I discuss romance between enemies more here.

Different Species/Beings
Love between humans and vampires or live humans and ghosts or aliens from different planets. Lifestyle and physical conditions complicate not only the romance but the consummation (think Buffy and Angel). 

How writers solve the romantic tension caused by the above situations goes a long way towards determining the romance novel's readers. Readers are attracted to certain types of resolutions and some resolutions are more satisfying than others. I did not include the approach of the romantic triangle. That's because I detest it.