J Lo continues on her birthday vacay without Ben in Portofino, Italy. She strolled through the city Saturday ... wearing a necklace with Ben's name front and center.

We're told Ben is actually heading back to U.S. soil, so J Lo's hanging out on the yacht without him.

Now that Ben's gone, J Lo's been on her phone nonstop, texting and FaceTiming to occupy her time.

As for the bling ... it's a custom Foundrae charm necklace that Ben gave Jen for her 52nd birthday.

Seems a shame J Lo's now solo on the yacht ... it runs $1.1 million a week, and has all sorts of toys and amenities. In other words, it's awesome!

Before leaving for the U.S. ... Ben joined Jen at a restaurant in Italy, but food seemed secondary as they were all over each other as diners watched.