Much as we might all speculate on this thread about what’s being left out of your friend’s story, I’d strongly advise you (and your DP) not to look into that or ask further questions. Anything other than a firm repeat of the basic boundary you’ve now set can (and no doubt will) be taken as a new opportunity to harangue you or escalate the sob story.
Boundaries are walls. You set them up, alert anyone who needs to know that it’s there, then walk away from your side of the wall back to your life. Don’t hang around your wall, getting worn down hearing the toddler wailing happening on the other side.
And any flying monkeys who pop over the wall to slyly scope the gossip or pressure you? They get the same short shrift. I use the sentence ‘Actually I’ve decided that topic is closed, I won’t be discussing it any more.’ Said in a calm, casual tone. Then change the subject or end the conversation.
I’d also be quickly planning some urgent house repairs/renovations to strengthen my resolve. Not cos I had to, just to give my boundary extra ‘bricks’. If you stop thinking of your home as having ‘spare rooms’, maybe others will too. They aren’t spare, they are exactly as occupied and useful as you want and need them to be. Rename them, redecorate them. You could probably use a meditation area with your current issues? Paint one red and hang a sex swing in it? That’ll send a couple of different messages to anyone hoping to stay. 