Matty Healy is in the middle of his own love story as his ex-girlfriend Taylor Swift marries the guy she dated after him ... with Matty taking his fiancée out for lunch on Taylor's wedding day.

The 1975 frontman was in downtown Los Angeles on Friday with his bride-to-be Gabbriette .... grabbing lunch and shopping while Taylor was in New York City getting hitched to Travis Kelce.

Matty and Taylor were linked in the spring of 2023, shortly after we learned of her breakup from her longtime London boy Joe Alwyn ... and after things between Matty and Taylor fizzled, Travis entered the picture.

Now, Taylor and Travis are celebrating their union with 1,000 people at MSG ... and Matty is in DTLA with his fiancée.

Gabbriette had her bachelorette party around the same time as Taylor's rumored bach party last month ... but no word on when she and Matty are walking down the aisle.

It's interesting ... Matty's keeping a close eye on his phone in these photos and video.

Unclear if he's keeping tabs on Taylor's wedding. 🤷