A husband who lost his wife in that culture did not experience the same social hardship that a widow did. A widow is unmarried and destitute. But a man who loses his wife is simply unmarried. He is not destitute. And I suspect that is why Paul and other Greek writers didn’t use the term widower to refer to such men. They were simply “unmarried.”
Another reason I think the Apostle Paul married is Paul uses the term “unmarried” two other times in this chapter to refer to those who were previously married. In verse 11, “unmarried” clearly refers to someone who was previously married but divorced. In verse 34, an “unmarried” person is distinguished from “virgins” who have never been married. That leads me to believe that “unmarried” in verse 8 also refers to someone who has been previously married. The gender is masculine in Greek, and when paired with “widows” it seems like Paul means to address those who were previously married but whose spouses have passed away.
And what does Paul say to these widows and widowers?
It is good for them to remain single, as I am.
I would tweak one small thing about the ESV rendering. It’s not as literal as it could be. There is no Greek term that corresponds to the word “single.” So if you just drop that word, it gives you a more literal sense:
It is good for them to remain…as I am.
“Remain” means to continue on in a certain state of existence. In their case, that state was one of widowhood. And Paul says “as I am.” This suggests that Paul is putting himself into the same category that they are. But it is not a category of singleness in general but a category of widowhood in particular. It is for this reason that many interpreters—including myself—believe that these words imply that the Apostle Paul married earlier in his life.
I don’t believe it is the case that Paul was never married. In fact, it would have been nearly unthinkable to imagine a never-married Pharisee. As an exemplary Pharisee (Philippians 3:5-6), Paul would have sought to fulfill the creation mandate to “be fruitful and multiply,” which means he almost certainly would have been married at some point. And verse 8 seems to confirm that he was in fact married but subsequently widowed.