It's hard. Heartbreakingly hard.
There are times it's amazing and he's the sweetest, kindest, loveliest guy I know, my best friend, soul mate etc
Then bipolar crashes the party - sometimes it's the impulsive spending of all savings on crap that's uneccessary that he argues is vital like comics or every single episode of some series, sometimes it's suddenly doing a million things at a million miles an hour - committing to anything and everything, occasionally it's coding, delusions, voices
Other times it's him not being able to get out of bed, having no empathy even with his toddler DC, him disconnecting from everyone and everything having no drive, no goals, no consideration, him being paranoid and defensive or suffering crippling anxiety and regret or those awful days wondering if he might actually go through with taking his life despite him promising he won't but he's told you how he'd do it etc
And it's so bloody hard to recognise when bipolar is crashing the party or if he's just happy, or understandably annoyed about circumstances as they happen - too often you don't realise what your in till you're right in the middle of it, so many symptoms could also be personality, so many people without bipolar do things my DH does - it's just the sum total that makes it up to "bipolar"
The meds can have side effects that feel worse than the symptoms sometimes too - when he can't think clearly enough to hold a conversation as its "foggy" or naps through your honeymoon, or kids show, or Xmas because he's so sleepy on them, or develops tremors, or can't feel any emotion at all because everything's numb. Sometimes side effects reach the point I think - actually I'll take the bipolar now over sluggish robot that they turn him into
Sometimes I wonder what I did marrying him, however I suffer OCD and depression myself and I know that he fights a horrific unkind illness everyday like I battle mine, and I admire him and I'm incredibly proud too.
Anything can happen in life - you could be with someone who develops anything - mental illness, terminal illness, brain injury etc and there are no garantuees. If you can see past the illness - and you could take the shit that comes with it because past the illness they're that lovely - go for it but go in eyes wide open and never shut them, ever.
The most important thing to do in a relationship with someone with a mental illness is actually not to take care of them but to take care of yourself imho (obviously you care for them but you put the most effort into caring for your own wellbeing and allow HCPs to take on responsibility that would floor you)