Relationships

Do I have a right to be upset?

I (21 f) am sorta seeing a guy (50m). We were coworkers who turned into friends and now sorta romantically involved. In the beginning when we first met, he didn't have a wedding band on so I stupidly assumed he was not married, and he never indicated that he was. It wasn't until I asked him just to make sure (because I have had men lie about that in the past) that he said he was married. When I asked why he didn't mention that earlier he said I never asked (which is true), but finalizing divorce (which is true as well). I then asked if he had any kids, and if so, how many. He told me he had two daughters, aged 10 and 15. Anyways we waited a few months for everything to finalize before starting to I guess "fool around". Recently however, I found out that he has another daughter who is 18. When I confronted him and asked why he never told me, he said she is his wife's kid. I don't know if I have a right to be upset, since we aren't technically in a relationship, and won't ever be because of various factors, but we are really good friends and always will be at the end of the day (and we like each other sexually). Any advice would be appreciated.

Do I have a right to be upset?
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