A source tells PEOPLE Scott Disick, 33, "was working to get Kourtney back"

It seems like reports of a reconciliation between Scott Disick and Kourtney Kardashian were too good to be true.

A source tells PEOPLE that Disick, 33, “was working to get Kourtney back but has given up again.”

Just last week, Disick returned from a vacation in Costa Rica with his ex and their three children (Mason, 7, Penelope 4, and Reign, 2), but immediately jetted to Miami, where he was spotted cuddling up poolside to models.

After the family vacation, another source told PEOPLE: “Kourtney hasn’t been happy with Scott for weeks. It has nothing to do with what he is doing in Miami right now. She just doesn’t like when he parties. He is an irresponsible dad when he parties.”

A Keeping Up with the Kardashians insider also added that Disick – who has struggled with alcohol abuse in the past – is, again, “getting out of control” and “partying a lot.”

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“She is not happy with Scott. She allowed him to come to Costa Rica for a couple of days so he could have fun with the kids,” the source said of Kardashian, 37. “Partying and making out with different girls publicly isn’t exactly the best behavior when you are a dad.”

The revelations followed a source’s January claim that Kardashian was “serious about making things work with Scott.”

Disick and Kardashian initially split in July 2015 after nine years together.