How do I (30M) approach telling a friend (38F) to stop pining after a taken man?

TLDR: A friend is wrecking her mental health obsessing about a taken man. How do I make her see reason?

I’m at my wits’ end and yesterday just walked out of a chat after five words because I couldn’t handle it.

I have this good friend of mine who was there for me when times were particularly rough for me and usually is the most level-headed in my small circle, but when it comes to this guy, it’s like talking with a brick wall. She is crushing on a coworker with whom she’s going (as part of a bigger group) to various nerdy events and it’s driving her crazy for almost two years now. But he’s married. Something she only seems to care about in terms of how it hurts her, given that she is still convinced that there are signs he is into her and that there is a “special connection” between them. However, whenever I asked for examples, she became terribly vague to the point of completely evading the question. The most concrete thing I ever got out of her was him saying once that he enjoys going to these events with her because his wife doesn’t share most of his hobbies with him. That’s it.

Not knowing him or their interactions myself, I told her at the beginning when she was severely troubled about how to behave around him that I can see only two options: Either that he’s willing to cheat on his wife, which would would make him untrustworthy and definitely not a good character, or that she’s mistaken and needs to deal with getting rid of that crush. And that means either focusing on just being friends or keeping her distance until the feelings dissipate.

I told her I was in exactly the same spot when I was in high school. My only crush I ever had was a girl who already had a boyfriend, so I swallowed those frustrating butterflies down so hard, I forgot about my awkwardness around her entirely for several years, until I suddenly got reminded about it in a carefree conversation about crushes and was like “Oh right, yeah, I had this once. It sucked.”. On the other end of the spectrum… well, my mother’s mental health got irreversibly shattered by my father cheating on her, which is a root cause for most of my current day pain having to take care of her. So I guess I am the worst possible person to talk about this kind of stuff.

Which I guess was the reason why she stopped talking with me about it after I had said all that, telling me I “just can’t understand” and that “it’s impossible to dismiss emotions” and that it would be wrong for her to try. However, she’s so absorbed in her hurt about this constellation that it’s impossible to talk with her about anything else, really. So after a year of only cryptic replies that she feels too bad to talk, she recently came back to opening up about it. The other day he was taking his wife along for an event, which depressed her greatly. I in my frustration told her to interact with the wife as much as possible, maybe things would clear up for her then. She claimed she can’t understand why she should and reacted irritated at the suggestion, saying she doesn’t want anything to do with her. Come to think of it, she never told me how their interactions ended up being… But what she did, was despairing at the fact that she was apparently pregnant. That was where I said “I’m going to swallow down my usual comments” and walked away, unable to deal with this anymore.

Still… I want to help her, after all. As I said, she is one of the best friends I have and it pains me to see her destroy herself like this for what seems like… such a pointless thing. Every conversation snaps back into how terrible she feels about it or that she had a fight with her mother (because her mother keeps telling her that she is just imagining things). I don’t see any good outcome, but it feels impossible to get through to her. Is there anything else I could try or recommend to try?