You mentioned that you're not sure about how to improve the one-sided empathy situation with your SO. So I thought it might be helpful to share some pertinent info that I've come across on HN in the past. I feel that the article and comment discussion on the "Intentionally making close friends" post (
https://news.ycombinator.com/item?id=33774353) may offer some actionable advice. Also, see the authors other post specifically on "debugging others" (
https://www.neelnanda.io/blog/30-debugging-others).
My own advice is to be direct with your SO about your needs / expectations not being met. I went through the same thing with my SO. We went to couples therapy for many years with no improvement, until eventually they realized it was serious enough of a problem to lead to the end of the relationship, prompting them to put in the necessary effort to change. Another poster mentioned Gottman "bids for attention" which is spot on as well. Both partners in the relationship need to show up for each other to provide emotional support. Some people are simply more used to receiving support and don't know how / aren't used to providing it. It should be made clear that this is unacceptable and needs to change, but also that you are willing to give it time and work with your SO to help them gradually improve their empathetic capacity so that they can be a better partner to you (and better person in general) and keep your relationship healthy.
I think it's also important to note that balance is key. You need to be mindful not to overload the other person's empathetic capacity by venting so much that they never have a chance to vent to you or to relax / recharge. If your SO is dealing with a lot of emotional distress themselves, they simply won't have bandwidth for you. We can never be perfect emotional support for each other, because each person deals with their own emotional distress / stressful events which temporarily limits their available empathetic capacity.