I would also explain the biology behind crying to him.

That sounds condescending and somewhat impossible when you have a diagnosis like bipolar. I had this friend who explained to me that she has attachement issues because of being bipolar and in an argument that she completely provoked she said to me: "I explained to you how my emotions work and you ignored them anyways."

What did I do? I didnt say goodbye kindly enough in her mind. She then proceeded to feel justified to "feel sorry for me" for being "an inconsiderate person and a bad human being".

Explaining a non-common behaviour "biologically" will put a lot of pressure on the other person and wouldnt be an approach a therapist for example suggests. She can point out why she feels the way she does and that her emotional reactions are overexaggerated but I dont see how you help your partner by trying to explain the biological framework of crying to them because clearly she is not showing a common emotional reaction when she cries frequently.