Thanks for writing your query.
After reading your post, it seems that your boyfriend is suffering from infection of the gastrointestinal tract.
He should be given antibiotic like Ciprofloxacin
500 mg twice a day along with antiamoebic like Metronidazole
400 mg thrice a day along with an antacid like Omeprazole
40 mg once a day before meals.Dicycloverine
can be taken for pain in abdomen.
He should have light meals with less spice and oil.
Maintain his hydration. He can be given hydrating fluids.
If the problem persists, get him examined clinically.
I hope this is helpful to you.