In the spirit of radical honesty why not talk about becoming fluid bonded BEFORE it happens! This kind of thing is a big deal that anyone sexually involved with any of the parties needs to be informed of so that they can make sexual health decisions for themselves. Just because an STI test came back negative doesn't mean that for sure everything is all good. There are window periods for a lot of STIs when they don't show up on tests. What you get, at best, is a picture of what someone's sexual health status was 6 weeks ago.
I'm not saying that in this case there is a risk of an STI but it is still something that as someone involved you need to know so that you can make your own choices around condom use ect.
Everything will be ok in the end. If it's not ok it's not the end.