Or HaChaim on Exodus 18:2/אור החיים על שמות י״ח:ב׳

1 ויקח יתרו חתן משה, Yitro, Moses' father-in-law took, etc. The reason Yitro is again described as Moses' father-in-law is that it was only due to his status as the father-in-law of such a great man that his peers did not prevent him from travelling to Mount Sinai and becoming Jewish. It was customary in those days to put heretics to death, seeing that the religions were all national in character and defection was equivalent to treason. Perhaps the Torah also hints here that though Yitro was known by an entirely different title, i.e. The Priest of Midian, he now spurned that title and wished to be known simply as Moses' father-in-law.

2אחר שלוחיה, after he had sent her away. The reason that the Torah is careful to describe Tzipporah's remaining in her father's home in Midian as: "after Moses had sent her away," needs to be analysed. Were it not for the Midrash we have quoted I would have to assume that Moses actually divorced his wife when he found that he was a full time messenger of G'd and could not devote time to his family. It was reasonable for Eliezer to remain with his mother seeing he had only just been born. Gershom too was presumably still a minor and as such an encumbrance to Moses in his mission. Moreover, according to the Mechilta on our verse Moses and Yitro had agreed at the time of his marriage to Tzipporah that the first born son would belong to the mother (to be raised as a pagan) whereas the other would belong to the father. At any rate, there was a good reason why both children had remained with their mother. When the Torah reports Yitro as bringing both his wife and his children to Moses personally, this is a tremendous compliment for Yitro. He did not need to expose himself to possible rejection by his erstwhile son-in-law. According to the interpretation in Shemot Rabbah 4,4 that Moses had not divorced Tzipporah but had relied on his father-in-law to see to it that the family would be reunited at the appropriate time, we may understand the words אחר שלוחיה, as referring to messages sent by Tzipporah in order to find out exactly where the Israelites were encamped. Yitro did not undertake the journey until after Moses had made it plain that he would welcome both him and his family.