While "Selling Sunset" star Jason Oppenheim and Jessica Vargas are no longer together, they did NOT break up over a disagreement about starting a family ... TMZ has learned.

Sources close to the former couple tell us ... the breakup had nothing to do with kids.

According to our sources, there was no single important reason for the split, but rather "a combination of small but eventually relevant compatibility issues" which led them toward friendship instead of marriage.

Jason has come under fire in the past for his stance on having children. His reluctance to start a family is thought to have been the reason for his split from Chrishell Stause in 2021.

Since then, the 48-year-old real estate broker has said he's open to the idea of having a baby, but he's not rushing into anything ... and, we're told Jess and Jason were on the same page there -- neither one is in any hurry to have children.

Despite his latest breakup, Jason is maintaining a friendly relationship with Jess. A witness told us the two were at the Halekulani Hotel in Hawaii Saturday, where they appeared to be good pals but showed no PDA as they chilled by the pool.

Jason and Jessica's split came after about one year together.