It sounds like life has really thrown you some curve balls and it seems like a tremendous challenge to cope with it all.
My mom is bipolar so I understand what a difficult disorder it is to live with. I also know that the medications for it are very hard to nail, and as was mentioned, prescription and dosage changes can make a big difference. For my mom, when she has a manic episode (which, for her, last weeks and occur about every 18 months), she need extra seroquil to help her sleep. For a while, her doctor tried taking her of Lithium because of its toxicity and because it caused her tremors, but no other medications currently available were able to adequately treat her symptoms so now she's back on it, but on a lower dose than she used to be.
How are you sleeping? Your disorder can really affect that, and sleep is a vital component in our abilities to deal with the things life throws at us.
One thing that concerns me is that you seem dependent on your husband. I understand how it can be much easier to cope when you have someone to lean on, but it can be very draining for that person. I'm speaking here as the child and primary support of a severely bipolar person. My other concern is that this can hinder your own ability to cope with the disorder.
For their part, it would be helpful for your husband and his girlfriend to hear what you've told us. The way you worded it sounds very reasonable and personal. It doesn't sound at all like an attack on them or anything, and that's awesome of you! There's no way to guarantee that they'll make any changes to the living arrangements, but at least if they know how your feeling, they can help support you better.
Another thing that really helped my mom was joining a bipolar support group. It's a disorder that's more common than a lot of people realize, and you might find a lot of help and support with other people who understand what you're going through.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker