And the notoriously busy Hollywood pair, who began dating in 2010, may have their packed schedules to blame.
"Honestly, their schedules were too hectic," a source tells Us. "It just got to be too much. I think they both just sort of knew they couldn't do it anymore. The travel and lifestyle got to be too much. Who knows if this is just for now, but I think this is for good."
In addition to hosting American Idol, Seacrest, 38, is also a radio host for his own show, On Air With Ryan Seacrest, as well as a red carpet host.
His 24-year-old love is similarly busy, promoting her latest flick Safe Haven, opposite Josh Duhamel, out in theaters just last month. She and brother Derek Hough, 27, are also currently collaborating on a Starz scripted drama about ballroom dance, titled Blackpool.
Last month, the former Dancing With the Stars pro dancer revealed that her Valentine's Day plans with Seacrest were going to be last-minute.
"I know there are plans, but I don't know what they are yet," she told Us in February. "I think I might be traveling. I'm not sure where. That's up to my boyfriend!"