OP, I notice you've absented yourself from this thread and I think I would too. There's a lot of judgment gong on here.
But, just in case you're still reading this thread, I have some nonjudgy things to add.
You might want to consult an attorney about the PI business. Just keep in mind that if you do anything about this, things might escalate. Also, a word of advice--in the future, don't answer your door to anyone you don't know. If someone says a package is being delivered, they can leave it at your door. If they say they need a signature, ask where the package is from, whom it's addressed to, and anything else you can think of. If you're not expecting anything, then assume the supposed deliveryperson is lying. If it really is someone delivering a package and needing your signature, they'll come back. And will leave a note on your door or mailbox.
Depending on what state your BF and his not-yet-ex live in, the divorce proceedings could drag on for a long time, especially if one of the parties involved is unwilling to compromise on significant issues. In this case, that would probably involve money and/or property, as I gather the children are no longer minors. That being the case, just consider how much of this you could stand and for how long. A friend of mine had a situation like this many years ago. Her BF was living with her, the divorce was in process, and his not-quite-ex made every single step of the divorce into a tremendous difficulty. My friend ended up breaking up with this guy when it finally got to the point--at least 5 years later--when she just couldn't deal with it anymore.
So you might want to consider putting at least a mental time limit on this. Either that or just realize that it could take forever. If this were me, I'd give the BF a time limit. That's not to say that you should do this--it's just what I would do. "You have to be divorced by Day X or it's over" would be my approach. If Day X arrives and he's just waiting for the final decree, then OK. But if Day X arrives and he and the not-ex are still fighting over whatever, then I'd be gone.
OP, if you can, send me a PM and we can talk if you'd like.