No I think they just show up randomly. You’ll have to look out for Lemmy posts to see if anyone from Mastodon comments. Next to their name is their instance, so if I were on Mastodon, my username would be something like: Resonosity@mastodon.social or something
A given group of people are not a monolith. While we do share a lot of similarities, we also all have the potential to be a little different from one another.
I hope you get a chance to find someone that will allow you to be open like that again. Sharing those emotions and having someone their to empathetically receive them is one of the most gratifying things as a human.