Thank you for asking!
What your boyfriend is having is a classic presentation of bipolar disorders and these mood swings need a proper psychiatric facility and an expertise of a psychiatrist. A very strict compliance to the medicines is advised. Get him to a psychiatrist and let them help you. What you are doing is a good human being sign and yes patience has a threshold and once crossed becomes intolerable even the if the stimulus is love of one's life.
It is the exam of your love and a troubled situation of your boyfriend. You can help him or leave him. Find hima good Bipolar facility. Sign him in and then it is your choice.You can move on or stick to the man you loved for 6 years.But don't expect from these mood swings some thing a normal human being would respond.
And it take a lot of time to get lithium levels in homeostasis.Put him on inhaled loxapine, some atypical antipsychotics and anxiolytics and benzodiazepines will help.
Discuss the options with your psychiatrist.
Take care