Goneback - untohergods - They were probably both idolaters, their having been proselytes is an unfounded conjecture. Chemosh was the grand idol of the Moabites. The conversion of Ruth probably commenced at this time.
Matthew Henry
Concise Bible Commentary
See Ruth's resolution, and her good affection to Naomi. Orpah was loth to part from her; yet she did not love her well enough to leave Moab for her sake. Thus, many have a value and affection for Christ, yet come short of salvation by him, because they will not forsake other things for him. They love him, yet leave him, because they do not love him enough, but love other things better. Ruth is an example of the grace of God, inclining the soul to choose the better part. Naomi could desire no more than the solemn declaration Ruth made. See the power of resolution; it silences temptation. Those that go in religious ways without a stedfast mind, stand like a door half open, which invites a thief; but resolution shuts and bolts the door, resists the devil and forces him to flee.
SDA Bible Commentary (limited)
Volume 1-7
15. Is gone back. Though attracted to Naomi, like Ruth, Orpah felt herself bound even more closely to Moab. Orpah’s return made Ruth’s decision more difficult, for now she stood alone.
Unto her gods. The god of the Moabites was Chemosh (see on Num. 21:29). Orpah may have temporarily adopted her husband Chilion’s religion (see Ruth 4:10), but if so, had now returned to idolatry.