I was waiting for something like this to come up, cheers!
Here is my idea of a FLOSS dating platform. I believe you can make a lightweight project by making it behave just like a profiles gallery, you can make use of pixelfed's code to speed up the process.
you can also let people fill their profiles with their federated social media content. by pulling profile pics, bios, and posts and linking them to the their dating profile.
As for direct chats, because of how sensitive this data is. you can let people add their instant messenger handles, like matrix, xmpp, briar, or jami accounts and carry on the chatting using those platforms. this will save the instance admins from a lot of legal responsibility.