It's tough when your loved one doesn't seek outside help. I think the best you can do is encourage him to get help when you think he needs it.
Ahh no! You should never stop meds without a doctor, because meds are what keep you stable. That's okay though - it's understandable. Sometimes we think we are better and don't want to rely on meds anymore. It might be a pride thing, especially given there is so much stigma surrounding mental illness. But again, it's crucial to let your partner know that like a broken leg, like diabetes, bipolar disorder is an illness and needs to be managed with meds + therapy. Does your partner have a psychologist they see? Finding a good psychologist he feels comfortable talking with might help with learning more about the condition, learning how to be okay with asking for help and that medication is necessary. Of course, it's a bit of a tough one because you need to convince him to see a psych, and that's hard for many people. But if possible, psychologists are really important in recovery.
In terms of the medication, it can take a couple of weeks for meds to kick in and start working. So it's very possible that the medication he was taking is good for him, but it just needed more time. In saying that, I'm not a doctor and I don't know what med he's on, but it might be a good idea to talk to your doctor next time he is prescribed a medication regarding the expected time for it to work. This may help your partner wait it out longer knowing that it will work at some stage.
I don't have bipolar disorder and my diagnosis is a bit iffy but my experience was as follows. I was diagnosed with unipolar depression and given antidepressants, which made my hypomanic. I didn't realise it at the time (just felt really elated and all the stuff that comes along with it!) but eventually it felt like my antidepressant just suddenly stopped working. My dosage was upped, and this led to more severe hypomania and hospitalisation. Now I am on a very low dose of antidepressants and I know I have a "diathesis to mood switching". So I just need to be very careful when taking antidepressants, but I don't switch without meds if that makes sense.
I have learnt from my experience that the most important thing with depression/bipolar/mania etc is to keep your doctor constantly updated as it can be very dangerous having untreated mania or depression.
Finally, please also take care of your own mental health as well.
Hope this helps