Anyone here do writing commissions? How do you handle extending large pieces?

So I have a smallish side hustle doing as the title says - a little writing commissions, mostly for NSFW kink settings. Most of those end up dried up and abandoned within a couple of thousand words, and extending those enough is fine, usually a browser tab open for half a night or two and you're done.<br><br>I've got a more recent one I've been writing, and I just hit 50k words on it without the actual story being over half done, and I'm just going utterly freaking mad trying to keep myself moving along on this massive as shit project. Anyway, I don't have the focus for it and I'm going utterly freaking mad, so I feel like you guys who do commissions or similar may have some suggestions for how to make it less agonizing. Anybody have any killer tips to share on this shit?<br><br>(I may be a shitty writer, and have a pretty low output, but it'd be bad business to tell me to fuck off, so ignore that if that's your first instinct)