Barry Allen / The Flash

Earth-One / Post-Crisis / New Earth

 * 1)  Iris West,  a news reporter, and Barry, were dating even before he became The Flash. They were later married, with him even then withholding his secret identity from her. She only learned he was The Flash because he talked in his sleep. Iris is later murdered by Professor Zoom.
 * 2)  Zatanna Zatarra  and Barry experienced some romantic tension in the time after Iris died.
 * 3)  Fiona Webb  is a woman Barry later became engaged to. When Zoom tried to murder her as well, an enraged Barry killed him, later being put on trial for murder. Because of this, he was unable to attend his own wedding, and his unstable bride later descended into madness.

Barry discovered that Iris is alive and living in the future. He traveled there and lives happily with her, the pair having a set of twins named Don and Dawn. Barry then died during the original Crisis. The twins, in the future, became superheroes called The Tornado Twins, but they too were killed, and Don’s son Bart came back in time to the present to become the superhero Impulse, with Iris following him back to the present.

After his return to modern day Earth, Barry renewed his relationship with Iris.

New 52

 * 1)  Iris West  remains his main love interest.

1990 TV Series (Earth-90)

 * 1)  Iris West  - Contrary to her portrayal in any other version, here Iris appears as an unideal girlfriend who breaks up with Barry in the first episode.
 * 2)  Tina McGee  is a scientist who helps Barry fine-tune his powers and become the Flash, then helping him in all his adventures. The two are good friends, and clearly bear stronger feelings for each other under the surface.
 * 3) Megan Lockhart was a private investigator who was hired to discover The Flash’s secret identity. She discovered it was Barry, and her employer turned out to be a bad guy who was later killed. She and Barry, however, took a liking to each other. Although she left town soon after, the two would have amorous connections on the two occasions she came back to Central City, the first resulting in her being attacked by The Trickster, and the second to attend the trial of the Trickster. Megan and Barry are seen kissing at the end of the season finale, which, due to the show's cancellation, ended up as the series finale.

It was later revealed that Barry and Tina had come to terms with their feelings for each other and married. However, she is referenced in the past tense, indicating that she has died, possibly in the grand attack on Earth-90 by the Monitor.''' '''

Arrowverse

 * 1)  Iris West  - It should be noted that the Flash show takes place in a secondary timeline, or a version of events created by someone going back in time and changing history. All we know about the primary timeline is that Barry and Iris grew up together as friends before falling in love and marrying as adults.

The the Reverse Flash then traveled back through time and murdered Barry’s mother when he was a child. Based on his friendship with Iris at the time, Iris’s father took him in. Thus, in this new timeline, Barry and Iris grew up in the same house together. Barry does not tell Iris how he truly feels about her, not through high school, or college, or well into their twenties.
 * 1) Felicity Smoak - When Barry travels to Starling City and meets Team Arrow, he and Felicity share an immediate attraction, but one that ends when he returns to Central City.

Iris eventually starts dating her father’s police partner, Eddie Thawne, while Barry becomes The Flash. Barry eventually tells Iris how he feels, but she states she does not feel the same.

When Felicity visits Central City, she and Barry acknowledge their feelings for each other, but they both know that they are in love with other people who do not requite their feelings (Felicity being in love with Oliver Queen). The two kiss once before she returns to Starling City.

Later, when Iris has learned that Barry is the Flash, and a tidal wave threatens to wipe out the city, she confesses that she does reciprocate his feelings. Barry is then forced to reverse time and stops those events from happening, and without such events to jar those feelings loose from her psyche, they go back to as before.
 * 1) Linda Park - During this time, Barry begins to romance a colleague of Iris’s, news reporter.. She soon learns that Barry still has feelings for Iris, and stops seeing him, but he assures Linda that he wants to be with her, and they form a relationship. However, Linda soon learns (well before Iris does) that not only does Barry love Iris, but she, however subconciously, loves him too, and she breaks up with Barry.

After learning Barry is the Flash (again), Iris acknowledges that she is beginning to think of him more in a romantic way. Nevertheless, she accepts Eddie’s proposal. Eddie, however, dies to save everyone from his evil descendant, the Reverse Flash. She and Barry do not even mention the possibility of romance again for several months.

In the second season, in an attempt to save her from the villain Zoom, Barry reveals his identity to Linda, who later leaves town.
 * 1) Patty Spivot - Barry bonds with policewoman Patty Spivot, and the two begin a relationship. Patty becomes very angry at Barry’s repeated unexplained absences. After accomplishing her longtime goal of catching her father's killer, she leaves Central City to go to school to fulfill her dream of becoming a CSI. As she and Barry part ways, it is revealed that she has deduced he is The Flash.

Now several months after Eddie’s death, Iris tells Barry she has feelings for him (again). The two begin a relationship and are later married (in what turns out to be a double wedding with Oliver and Felicity).