"Charlie feels awful," the friend tells PEOPLE. "He let himself down by drinking ... [And] he wants to be with his kids."
On Wednesday, Mueller's lawyer told PEOPLE that she hopes to save their marriage, a sentiment echoed by the couple's pal. "[Charlie] has two little boys and he does not want to get divorced again," says the friend.
Mueller's lawyer Yale Galanter filed paperwork Wednesday to modify the protective order against Sheen so that the couple can see each other and start to work out their issues.
In the meantime, Sheen, 44, has been laying low at home in Los Angeles, while Mueller, 32, and their twin sons remain in Aspen, Colo. "He's trying to take it easy before he has to go back to work on Monday," says the friend.
As for the knife that Sheen allegedly held during the couple's argument, the friend explains, "Did he have a knife with him? Yes. It's a pocketknife that his dad gave him 22 years ago, which he always carries. It's not like he got a kitchen knife and went after her." Mueller told police Sheen threatened her with the weapon, while Sheen denied that claim in a police report.
For now, the couple needs "to take a week off to cool down," but they hope to make amends, says the friend, adding, "Brooke and Charlie care for each other."