And it's sad when you know it's your heart you can't trust
There's a reason why people don't stay where they are
Baby sometimes love just ain't enough."
Usually, the hero will go to great lengths to protect his Love Interest from the dangers involved in what he does, from keeping secrets from her to breaking up with her for her own good. Sometimes, however, the hero will choose to be honest and tell her everything, trusting her to make her own decisions about what's best for her. Usually when that happens, the love interest will bravely and loyally stay by the hero's side.
But sometimes, the love interest will decide the hero was right: she really can't handle it.
Maybe all that stuff about ghosts, witches, and demons is just a little too scary. Maybe she's sick of being kidnapped by the villains. Maybe the stress of the long nights waiting for the hero to come home from his missions is just too much. Whatever the reason, loving the hero just isn't enough to overcome everything that comes with being part of his life. She's out of there.
This is not necessarily a very "romantic" trope, but in some situations, it can add a tremendous note of refreshing, if uncomfortable honesty. Can overlap with I Want My Beloved to Be Happy if the hero graciously sends her off to another life (and another love) rather than beg her to stay in a situation she's not suited for.
The counterpart to It's Not You, It's My Enemies. A subversion of The Power of Love. See also The Masquerade Will Kill Your Dating Life, All Love Is Unrequited and Differing Priorities Break Up. A related trope is Grief-Induced Split. Contrast Love Transcends Spacetime and You Are Worth Hell.
- Sailor V and Kaitou Ace in Codename: Sailor V are mutually attracted to and love each other, but can never be together because they turn out to be on opposite sides of the conflict. Ace, or rather Danburite, is unable to reconcile his orders to defeat her with his desire to win her heart, and Sailor V knows she will ultimately choose her duty to Princess Serenity and defeating the Dark Kingdom over any personal feeling she has. She ends up killing Danburite.
- Me And My Gangster Neighbour: Ayako and Aoi are obviously attracted to one another, but when it is revealed that Aoi is a gangster, Ayako tells him that she'll be keeping her distance as long as he remain in that profession.
- The song "Life Waster" by Corpse Husband has two young lovers from very different backgrounds meeting and bonding over their various physical and psychological traumas, only to have their differences and personal issues drive them apart. Worse yet, early in the song it seemed like maybe they managed to part ways on good terms, but as later verses show, any remaining positive feelings have apparently given way to anger and bitterness.
- Tears for Fears: The song "Swords and Knives" features the verse "And it's sad love's not enough to make things better".
- The Imagine Dragons song "Polaroid" is seemingly about a man who considers himself a complete failure and compares himself to a seemingly perfect lover, but that they can't fix him - nothing can, he has always been this way - and their love can't fill the fundamental void in him either.
- Elisabeth: Before their wedding Franz Joseph warns Elisabeth that she won't find it easy to be empress. She thinks she can cope with it, then immediately after the wedding she discovers she has to deal with Death stalking her, a mother-in-law from hell, and the pressures of life in the Austrian court. Things go from bad to worse for her from then on, including Franz Joseph cheating and two of their children dying. Finally Elisabeth breaks up with Franz Joseph for good in "Boote in der Nacht". Her first line in the song translates as (roughly) "Love can do much, but sometimes love's not enough".
- The first act of Sunday in the Park with George. Although George Seurat loves his adoring mistress Dot very much, he is too occupied with his masterpiece painting to pay attention to her. She eventually leaves him with his baby daughter for a more caring partner. Before she leaves, she visits him at the park and fails to tempt him to see his infant daughter. George simply explains to her that the baby will have an attentive father now.
- Batman: The Animated Series: Similar to the comics example above, Two-Face's fiancée, Grace, never really gives up on him, either.
- Clayface also had a lover who tried to restore him to human form... but after he crosses the line and murders his own daughter, she's never seen again and it's implied she gave up on him just as thoroughly as Batman.
- In Batman Beyond, during a conversation about Terry's girlfriend, an elderly Bruce Wayne admits that he had relationships with a lot of women over the years, including known superheroes like Wonder Woman all the way down to Barbara Gordon during her days as Batgirl, before she moved on to follow in her father's footsteps as a police officer. He explains that all the relationships ended because the women gave up on him after realizing he would never give up being Batman and settle down with them. He tells Terry this now that he is Batman as a warning about his own relationship.
- Maria Rivera from El Tigre: The Adventures of Manny Rivera was unable to see her husband Rodolfo/White Pantera constantly in mortal danger... this might seem a little strange considering that she herself used to be a superheroine herself, Plata Peligrosa and not exactly of the defensive style on top of that. However, Maria gave up being Plata Peligrosa because the glove she used would often put her through an uncontrollable Power High. Fearing for the safety of those around her, Maria quit because the damages outweighed the benefits. However, according to Word of God they remarried once Rodolfo finally retired from heroing.
- In Superman: The Animated Series, Lois Lane breaks up with Bruce Wayne for essentially the same reason Silver St. Cloud did in the comics. Though—as we see in Justice League Unlimited—she doesn't have the same issues in dating Clark/Superman (or has gotten over them).