Welcome miss_random to the forum,
thanks for making your first post. You are very caring girlfriend and very kind to want to know how to help him.
Living with someone with bipolar is tiring and confusing and living with bipolar is exhausting and confusing too.
When your boyfriend seems angry with you, he is angry with himself and very confused.
If you can talk to him when he is lucid , that is the best time to ask him how to help him when isn't well.
I have had bipolar for over 40 years and I know when people asked me questions when I was unwell I can't think properly or I forget.
There is a thread called This bipolar life , that you are most welcome on. It is a very long thread , and the first post may give you an insight into what having bipolar is like. You can browse the thread and post and ask questions if you like.
Everyone who has bipolar experiences in a different way.
I understand you feel like you are walking on eggshells but I guess he really appreciates you are there for him.
Sometimes all you can do is to sit and listen or hold his hand . Often you don't know what you wnt and everything irritates you. You push away loved ones and that makes you hate yourself.
You need to look after yourself and get support for yourself. It is not easy. There are threads about living with someone with bipolar which may help you.
Thanks for reaching out. You are not alone and we are here to support you.