# he must not diminish her food, clothing, or her marital rights

"he must give the first wife the same food, clothing, and marital rights she had before"

# must not diminish her food

"must not take away her food" or "must not give her less food"

# or her marital rights

"and he must continue to sleep with her as before". This includes things that a husband must do for his wife, including sleeping with her.