You ask a good question!
It is not enough to read the lines of a biblical text; you must learn to read in between the lines as well. Some aspects of a story are only hinted for a reading audience. With a healthy curiosity, one can often sleuth the untold story of a biblical story.
It pays to have the curiosity of a Sherlock Holmes, and here is an interpretation that I believe the great detective would probably have approved.
When God first spoke to Moses about becoming His leader for the oppressed Israelites, he went to his father-in-law Jethro and told him all about the news. In Exodus 4:24-26, we read a short story about Moses’ near-death experience and how Tziporah, Moses’ wife, saved the day by performing circumcision on one of Moses’ sons.
On the journey, at a place where they spent the night, the Lord came upon Moses and sought to put him to death. But Zipporah took a piece of flint and cut off her son’s foreskin and, touching his feet, she said, “Surely you are a spouse of blood to me.” So God let Moses alone. At that time she said, “A spouse of blood,” in regard to the circumcision.
Tziporah’s words might have been a criticism to her husband. Although she was a Midianite, a member of the Abrahamic clan, none of the ancient peoples of the ANE ever practiced infant circumcision—only the children of Israel. Circumcision rites were basic to all the marriage rituals; circumcision of males typically occurred at puberty—the age when a young man would take a wife. Tsiporah had no problem with that tradition. However, she and her father rejected infant circumcision; the Israelite rite seemed excessive and, not to mention, dangerous! Ironically, Tsiporah performs the ceremony—howbeit very reluctantly.
Moses argued that circumcision had to be performed when the child was eight days old (Gen. 17:12). Failure to receive circumcision meant that the boy would be "cut off from his people." God expected that Moses , of all people, must be a leader and practice this tradition openly and proudly.
There is much more to this little interpolation than what meets the eye.
Contextually speaking, Moses’ behavior in Exodus 4:24-26 seems very strange for other reasons. How could Moses entertain the idea of taking his family to Egypt? Egypt wasn’t exactly like Disney Land! This idea does have support in the Midrash. According to the Sages, Jethro tried to convince Moses "We are distressed over the plight of those who are there, why should you bring your family there?" 
As a leader of an oppressed people, Moses would have certainly endangered his family had he brought them there with him (Ramban). All of this might explain the reason why Moses or his son took ill. The family illness may have been God's way of keeping Moses's family from having to endure the hardship of slavery in Egypt.
In the end, Moses sends his family home to his father-in-law. Tsiporah most likely felt resentment toward Moses for choosing God over his family. The Sages indicate that when the text later says that Jethro brought Moses’ family out to greet him shortly after the Exodus.
Note that Moses does not go out to his wife and children as one might have expected. Jethro takes the initiative and brings about a reconciliation and reunification of Moses fractured family.
All seemed well . . .
Later, in the Book of Numbers, we read about a strange development in Moses’ family.
Who was this mysterious new woman in Moses’ life? Did Tsiporah finally get fed up with Moses for neglecting his family? Did they fall out of love?
Inquiring minds really want to know!
Some of the medieval commentaries like Ibn Ezra and Abarbanel contend that Tsiporah may have died and Moses remarried—and this was something that Miriam did not approve because the Cushite was black-skinned! Rashi and others say that the Cushite was really Tsipporah and Moses had neglected her after assuming the role of leadership. When she heard about young prophets Eldad and Medad, the legend asserts that Tsiporah felt bad about the prophets’ wives. She mused, “Their poor wives will suffer!”
If rabbinical legend is correct, the Midrash teaches us that Moses was a great husband, but a lousy husband and neglectful father. Does it not seem strange how the Torah speaks much about Aaron as a family man, but Moses as a family man is almost completely absent in the Torah narratives about Moses?
Does the story end there? What ever became of Moses’ children? Or for that matter, his grandchildren?
Here’s the rest of the story . . .
Rabbinical tradition argues that Moses’ grandson ultimately became a pagan priest and his narrative is recorded in Judges 17 & 18!
The Book of Judges, Chapters 17 and 18, may hold the key to answering these questions, which speaks about Micah’s idol, which was introduced in the tribe of Dan; he hires a Levite from Bethlehem to become his personal priest (Judg. 17:5-13). In Judges 18:27, the biblical narrator reveals the identity of the Levite mentioned in Judges 17 and he is the grandson of Moses, for according to Exodus 2:22, Gershom is the son of Moses! The biblical scribes deliberately changed the name from Moses to Manasseh, one of the most notorious Judean kings who introduced idolatry during his rule. The superscript letter “n” helps to confuse the reader so that he will not know that Moses’ grandson became a priest to idolatry. Beyond that, the verse concludes, “Both (Jonathan) and his sons were the priests to the tribe of Dan until the day of the exile of the land” (Judges 18:30).
All of this goes to prove that even the most excellent of prophet had feet of clay when it came to parenting. One would think that Moses would have deeply impressed his son Gershom to remain as a true son of Israel, and worship YHWH alone—but evidently, his son must have been out playing with the other young Israelite young people. This lesson did not sink in.
May this sobering thought may keep us humble.
The personal life of a spiritual leader—regardless of one’s religion, often places a heavy burden on the family. Jokes made about clergy’s children are proverbial. In the Bible, we discover from the Book of Genesis how family dysfunction affects even the most righteous and pious individuals of the Bible. Just look at the family histories of the biblical patriarchs.
What about Moses? Was he a perfect parent? Was he a perfect husband? I think he had many of the same issues that modern couples experienced--especially when they are not equally yoked.
Was your teacher correct? I believe he probably was, even though he did not explain how he arrived at his conclusion.
 Shemot Rabba 4:4.