Not rememembering certain things is typical of people with bipolar disorder.
Please also note that whatever he is doing like fighting with you or leaving home without any information are due to his illness. He is not what he is doing right now.
Bipolar disorder can be treated effectively and people can lead productive lives. Once he comes out of this episode and knows what the problem is and fully follows the doctors advise - he can recover.
Anyway , since you have admitted him into a hospital , you need not worry about him running away. Get him out of there only when docs say so. Help him to follow mediacation advise and recover.
Love & affection helps him a lot. It is definitely a demanding task. But try.
No need to think of having children etc now and worry on that. It is too early.