You are giving way too much concern to what might make him feel bad than to what you need to do for you. How you handle this will influence how you handle the next situation where someone wants to gain unwelcome access to you . . . and the one after that and so on. You would be smart to start now making it a habit to not let someone you owe nothing to get the idea that you can be imposed on. You worry about not wanting to seem rude. This guy also has an obligation to not be rude toward you. If he doesn't back off, after you signal your disinterest, then he is the rude one.

Whether you tell a white lie or not is really unimportant. It's important that you understand that you are free to make a fake excuse or simply say no. Either is ok.

I would say that meeting him for coffee just encourages him to want more contact. When you really don't want to do something, it's probably best to just not do it. It can be noble to make a sacrifice and go to trouble doing something to promote another's welfare. This is not that kind of situation.