I want to ask my friend if he's free because no one else is.
Are you sure he's the only one?
Yes, he is the only one who was available.
It's good to ask a friend if they're free before making plans. They'll know you're being considerate and may want to hang out with you even more.
It would be too much of a hassle to do that.
You shouldn't make plans before seeing if a friend is available. It's really inconsiderate of their time. You should check with your friend first, so that he knows you respect him and wants him to be included.