Being FORCED to go to a gender reveal

I’m not sure how to feel about tomorrow. Little back story before I fiancé and I have been together for 6 years. Been trying to have a baby for 4. I’ve taken multiple negative pregnancy tests with high hopes then a crushed heart everytime. My gynecologist cannot figure what’s wrong she always says everything looks normal and comes back normal. Well, the day I took a test and it was of course negative we went to my fiancé’s where his brother and his girlfriend live and she says IM PREGNANT!!!!! And it about killed me inside. They both live with their mom no jobs sleeping on a air mattress his brother still smokes weed and has no ambition to quit for a kid. He didn’t want a kid. She knows I have been trying with no luck and EVERYTIME I’m around her she says stuff like “you should never get sucks” or she whines about being able to have a baby then takes it back and tells me she’s sooooo lucky and that it’s a beautiful gift. So tomorrow is the gender reveal. I have stayed away from her for months. But my fiancé says I HAVE to go. I don’t want to. I’m not emotionally ready. I’m depressed. Been depressed. Nothing against her but I feel like it should have been us. We are financial sturdy and have our own house and we both WANT a baby. We have two spare rooms empty ready to have a family. Idk how I’m gonna handle tomorrow. Please give me your opinions on what to do.