Despite his misgivings, Obi-Wan knew that sitting around the Temple trying to concentrate on his lessons wouldn't get them done any faster than sitting around all afternoon, had. Ignoring the voice in his head which was telling him not to, he told Atian, "Yes."
It was relatively simple for the two Padawans to sneak out of the Temple. No one knew they were not supposed to be leaving -- and Atian actually did have permission to go -- so all they did was walk out, calmly.
Obi-Wan's misgivings didn't ease as they boarded the shuttle for the party, but he kept quiet. An evening out would be good for his state of mind, and when he returned the worst he'd face was a lecture and extra boring duties to remind him why he should obey his Master.
By going -- he told himself over again -- he would gain a few hours' respite from his troubles. And that would be worth a lecture and tedious duties.
The party proved to be a success, as far as distracting Obi-Wan from his troubles. He talked, laughed, danced, and drank far too much punch. Someone early on had warned him the punch was spiked, but as the evening wore on he found himself not minding.
At last Atian came and jogged his elbow. "We're headed back for the temple, Obi. Almost curfew."
Obi-Wan blinked owl-eyed at his friend. "Already? But I'm having fun."
"You can stay if you want and come back on a later transport," Atian offered. "Biloa is going to be at the door. She'll let you sneak in."
Obi goes with Atian.