That commentary is highly speculative, mostly consisting of questions about possibilities. There also seems to be an assumption of monogamy, with Moses' second wife being assumed to be a replacement for Zipporah, rather than an unrelated separate relationship. I get the feeling that the second marriage itself encouraged the thinking that Zipporah was divorced, as he seems to think she was gone for good, not returned later by her father.I also found this tonight here in which he quotes another commentator Ba’al HaTurim as saying that this was the case.
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