Did you two every discuss the possibility of fluid bonding with others someday? Is your live in partner uncomfortable at all with any of this other partners sexual practices? If so I imagine you have a clear statement about how you are going to address any concerns. Is he clear that the relationship no longer feels casual and you love him?
If he isn't, I'd make that clear and wait a couple of months to bring up fluid bonding. If he is, I'd probably wait until I felt the breakup wasn't fresh and raw. Do you know if you're willing to bring up the discussion but not have him make a decision about how he feels about it or act on it for awhile?
I brought this up with my ex husband over 7 years ago, it was awkward, sure. The gist was "I'd like to stop using condoms with Adam. These are the reasons why - I feel _________ and it would be _______. He's willing to use condoms with all other partners, he gets tested regularly and I trust him. I don't know how you feel about it, but it's been on my mind so I wanted to talk about it"
If your other partner would not be using condoms with other people obviously I'd just insert whatever safe sex practices and risks would be in place to your live in partner. If someday I want to talk to Adam about fluid bonding with somebody else I'd be saying just about the same thing.
Happiness will never come to those who fail to appreciate what they already have.