Should I tell him?

Yes but her son doesn’t know his mother is gay @R5000

@Dedicatedmom Then you have no part in outing her to her son. Unless you want to lose them both.

All are adults. But will this become a childish issue?

@R5000 This isn't anything to do with childish. This is one woman's privacy, possibly being violated.....for what? If this woman wanted her son to know she was gay, she would probably have told him before now. When she's ready to do so, she will. But, if dedicatedmom tells her friend's son that his mother is gay, she is taking away that mom's right to her privacy and to her right to be the one who discusses private matters with her own son.

@Serenitree over sensitive much?

@R5000 It's a delicate issue and a matter of discretion. One cannot be "over-sensitive" regarding parent child relationships. It's the mother's right to come out to her own son when and IF she chooses to. It would be wrong of the poster to out her.
Part of "finding oneself" is moving at one's own pace.

Go up. Look. I had a question mark......

@R5000 ..and your question was answered.