Matty Healy On Shopping Spree While Taylor Swift's at Jack Antonoff's Wedding

Taylor Swift certainly had love on her mind at Jack Antonoff's wedding, but while that was going down, her ex-boyfriend Matty Healy was on the other coast ... laser-focused on music.

We've learned The 1975 frontman was browsing around a music shop, Norman's Rare Guitars, in Tarzana, CA on Saturday ... the same day Taylor was watching Jack and actress Margaret Qualley tie the knot.

The musician swung by the store with his tour manager, ultimately buying a guitar -- unclear how much dough he put down for it, but it looks like a pretty sweet Fender 6-string.

While Matty was shopping on the west coast, Taylor was at the big ceremony on the Jersey Shore ... where, as we reported, droves of Swifties flooded the main street on Long Beach Island to get a glimpse of the singer.

You'll recall, Matty and Taylor were briefly an item, spotted hanging out quite a bit in May, and he even snuck into her NYC pad ... but sources told us Taylor was "single" again in June, although it's unclear why they called things off.