They might let him sit due to his leg problem. I dont suppose they can force him to give evidence,but he would be losing the chances to speak for himself.

Under legal systems that derive from the English system, a person does not have to testify against himself/herself. Under ANY system a person always tries to make themselves look good.

YES! He will have to take the stand in order to put forward in his own words

the events leading up to, during, and after the shooting.

Also, how well their relationship had been going etc.

He hasn't got a leg to stand on.