False Soulmate

""'Follow your heart.' Ha! – Sometimes the heart sends confusing messages. Contemplation, counseling, friends, and readings can help us sort our true convictions from the false ones, though we flat-out disagree with the advice sometimes. Yet even THAT may tell us a lot. We usually need help sorting it out. But there’s always a lesson!""

- Mary Rose, Beware the False Soulmate (California Psychics Blog)

A False Soulmate is a person who someone has a deep romantic Love Interest for, but the relationship is for some reason not meant to be, perhaps because of the Love Interest not sharing the same feelings, incompatibility, or misjudgment of character and/or the relationship ends up being a failure or catastrophe because the Love Interest's personality or behavior has changed in a negative way (e.g. the Love Interest may be unfaithful, a user, a criminal, mentally unstable, or a drug-addict). This may stem from Puppy Love or personality traits that the Love Interest either had or had more of when they were younger.

Anime & Manga

 * Athrun Zala and Cagalli Yula Athha went down this path in Mobile Suit Gundam Seed Destiny. In SEED, they ended as the Beta Couple to Kira and Lacus. In Destiny, they eventually grew apart due to Athrun getting involved with ZAFT again, Cagalli's position in the Orb government (and the stress involved), her Arranged Marriage to Yuna Roma Seiran, and differing views on Chairman Durrandal's real goals and motivations.
 * While there seemed to be a bit of hope for the two reconciling near the end of Destiny, Word of God has stated that they're "just friends now".

Film -- Animation

 * Shrek: Played straight when Princess Fiona believes Shrek is her True Love because he rescued her. Cue hysterical laughter from Donkey and Shrek. Shrek solely rescued her for Lord Farquaad so he could get his swamp back. Subverted when.
 * Monsters vs. Aliens: Derek to Susan. He is a vain weatherman who is more interested in furthering his career than in his fiancée's needs, and after Susan spends the first half trying to win her freedom and return to him, he rejects her because he isn't interested in having a wife who overshadows him, in more ways than one.

Film -- Live Action

 * Sleeping With the Enemy: Martin is a wealthy investment counselor who's charmingly handsome on the outside, but his true colors don't show until after he and Laura are already married in the beginning.
 * Mrs. Doubtfire: Daniel and Miranda Hillard divorce and never get back together.
 * Forrest Gump: Jenny to Forrest.
 * Wolf: Charlotte Randall to Will Randall. He separates from her after he discovers she's been cheating on him, but before she gets killed.
 * Stardust: Victoria to Tristan. She's a Spoiled Sweet and geniunely stuck-up brat who is sweet to Tristan more out of pity than any strong feelings toward him, even though he wants to propose and spend the rest of his life with her. He later falls for  instead, who actually loves him in return, once he realizes this.
 * Enchanted: Towards the end, True Love's Kiss indicates that the couples  aren't meant to be with each other, but that   are.