The US songwriter, 27, has been renting a house in North London while she has been seeing Joe in the UK.
People flew to Florida to be with her, but Jai didn't," the source said.
"Ariana just felt he wasn't there like he should have been."Meanwhile, the rapper was engaged to star Naya Rivera but the pair ended up splitting in April after Big Sean, "made the difficult decision to call the wedding off." Following the public breakup, Rivera shocked everyone by marrying actor Ryan Dorsey in a super secret Mexico wedding three months later.
And Taylor has gone to great lengths to ensure her visits have remained unnoticed.
The source added: "Taylor has flown in via private jets and her security has made it a military-like mission to prevent her from being seen.