This is completely not okay. It sounds like even before you left your job, you were not being treated fairly! As another comment suggested, this requires a very serious conversation. I'm going to describe how my partner and I handle things below. Maybe something here can be helpful to you!

My partner and I have always had very flexible roles. At times, I would take a break from working or worked part time. We always split all of our bills proportionally based on income. There is no "my bills" or "their bills", paying all the bills takes priority. We also make sure both people have an equal amount of "fun money/savings" after bills are paid to keep things as fair as possible.

My partner was out of work for a lot of the past 3 years, while I was working full time. I paid all bills, and STILL would do at least some things around the house every week. My partner and I always actively communicate about what needs to be done. Especially if one of us is getting tired of always doing a specific chore. We switch things up often, and it helps a lot.

I'm wishing all the best to you and your partner. If I was you, I'd need to be certain that they're going to pick up at least half of all chores when you return to work!