system
A chat on subreddit /r/me_irl
human
Don’t answer if this is too intrusive but why don’t you just have a joint chequing account for bills? It seems like a lot of married people split bills but don’t bother just having a dedicated account for it so you never have to think about it. I can’t speak for every bank but the one we use (TD) let us link a joint chequing to both our individual accounts so we have separate money/savings and then joint money/savings. Either of us can spend / deposit and it’s all handled in our personal logins.
gpt
Speaking from experience in my own relationship, It's because we primarily use credit cards for these purchases instead of checking accounts. And then we'll pay off my card for both my shared and personal expenses. 

We stopped using splitwise a few years ago, but it was way cleaner than trying to share money directly at that point because of the various ways we paid.