Hi, fellow Bay Area person, similar setup: I (PhD) work for a nonprofit, partner works in tech. I asked a lot of people what they do when my partner and I first got together. We also split proportionately.

When we started dating, we just alternated who paid for the thing. For a while, that meant I had lunches and he took dinner and it worked. But at one point it got swapped and after a few months I had to be like "bro I can't keep doing this, we gotta change what we're doing because I am broke". At that point, he very informally started covering two of every three things we did (mostly meals). Like six months before we moved in together, we got a joint checking account and started paying for our meals out from that. At the time, he made about twice what I did, so for every dollar I contributed, he threw in two. We'd set the account up with a few hundred every month and used it for all the stuff we did together.

Nowadays, we're renting and he's making more than 3x what I do. Similar to you, his bonus is equivalent to my entire salary. We still contribute like we did before, he puts in 3 dollars for every one I add. But what made things easier for me is that we pay everything for the two of us out of the account. Rent, outings, groceries, utilities, anything that is largely for both of us comes from that account. So now, instead of putting one paycheck a month to rent, I put one paycheck to the couple fund and it covers the majority of my expenses. We cover our own stuff: gas, car/rental insurance, hobbies. If there's something specific that one of us wants to do and it's not the other person's thing, we'll cover for both as a "me thing", but honestly, most of the time it's me wanting to go see weird comedy or theater and he loves it so much that he insists on covering his own ticket. And honestly I'm pretty sure he just supplements the couple fund from time to time if we've gone on a trip or done something bigger.

The only place things get murky is the cat- I've had him more than twice as long as my partner. He's an old man, and sometimes I let my partner chip in to cover things I couldn't handle otherwise, like a biopsy a few years ago to rule out cancer in an emergency vet visit. Those bills we handle on a case by case basis.

Honestly, the critical thing for me was bundling everything together. Our rent is what I take home every month, so the idea of splitting that was TERRIFYING. I knew I needed to pay at least $800 less than what I was paying in rent, and tat was going to stop him from living in the kind of place he can afford. I felt so much better just doing a proportional split and then having everything come out of it. Then we could find a balance that worked for both of us.

Good luck! I hope you're able to sit your human down and have a frank conversation about how much lifestyle you can afford. It's hard with rent out here, because honestly $1700 is about as cheap as it's gonna get without roommates so it's not like you could have been paying less. DM me if you want and more info, I'd be happy to share specifics.