1. He's a worrier. He agonizes over every decision he has to make.
2. He agonizes over every project his manager assigns to him. He's such a perfectionist.
3. Sally has agonized over this assignment since the beginning of the semester. It's the most challenging one she's done so far.
4. Would you stop agonizing over this situation? Everything will work out!
5. They have eight kids. They always agonize over who(m) to take on vacation.
To agonize over something is to worry, suffer, have a tough time dealing with something.