Pete Wentz and girlfriend Meagan Camper put on a united front when they stepped out in Hollywood on January 21 with his three-year-old son, Bronx, but Star magazine can exclusively reveal that there is sadness in paradise.

Privately, the pair were hit hard when Meagan suffered a miscarriage  around Christmas, her grandmother Sherrilyn Camper exclusively tells Star.

Meagan struggled during the pregnancy, with little support from the rocker, 32, according to Sherrilyn. “(He) abandoned her right off the bat... He wasn’t very much help, that’s for sure,” Camper explained.

As RadarOnline.com previously reported, Ashlee Simpson’s ex-husband began dating the pretty brunette model last September, and the couple has since enjoyed family bonding time with Bronx.