My husband has bipolar and awful anxiety, especially socially which is a big problem at times for him.
His mania is very well controlled. He gets it in the form of agitation and obsessive behaviour now, but no highs in a way you would assume he would. The switch between a decent mood and extremely low mood can be quick and every day can be different. I say decent mood because his mood is always lower than it should be.
Lows are a massive issue and after 20 odd years of many different meds we know they will always be poorly controlled.
It's difficult at times. I have to try and spot when he is heading towards a crisis and I do it well, but that's after many years of learning and having to become an expert in his illness. I have had to fight for him to receive help when he couldn't do it himself.
My advice to you would be if you let his moods affect yours you are in trouble. I am an expert now at not letting his moods change mine. It helps that he is a wonderful gentle and kind man and he doesn't take them out on anyone, he will take himself away if he is feeling grumpy with other people and I expect nothing less. You have to be strong and resilient. Over time it becomes easier in many ways because I instinctively know what he needs and when but it's still a tough road to travel at times. It's also heartbreaking to watch so you have to be able to bounce back yourself and be able to protect yourself emotionally.
I would marry him all over again though. He is an amazing man and the good outweighs the hard periods. However, I would tell anyone who is dating someone with bipolar to take the relationship slowly because you don't always know how awfully their condition affects them and before settling down you need to be quite sure you have the personality and strength and actually want to deal with the things you will be dealing with. It is not for everyone. It's difficult no doubt about it, and my husband has never let his moods change how he treats anyone and he always treats us with love and care no matter what.
He is going through a very good period right now, he is doing extremely well but it can take one day to change it.