What do you guys really mean when you say you don't know what you wanted?

This is easy. He's just not that into you.

But don't hold that against him. If it was in his power to CHOOSE who he likes and who he doesn't like, he would obviously CHOOSE to like you the most, since you're the one he's with.

But alas attraction is not a choice. It's not a choice for you either. Would it make sense for a guy to hold it against you for not choosing to like him? No, of course not.

When a guy says something like this, just understand that he does not want to hurt you by saying point blank, "I don't like you that much". It doesn't mean you are a worthless person. You just don't attract this particular person that much. Fortunately, there are 6 billion others to choose from.

I'm going to have to agree with wiseman when I say that this question is indeed pretty vague. The context with which this line was used is basically pivotal as to what the guy meant when he said it.

It could be like wise said, and it really is just an excuse used to hide the true meaning (which is likely shallow at best). Or it could be a sign of something else.

Sometimes things like this are signs that a guy isn't ready for whatever turn the relationship making. The biggest example here would be a matter of a change in commitment. Some guys just aren't mature enough, or just simply not ready to move to a certain level of commitment, and this is perfectly normal behavior up to a certain point and age (although climbing towards the 30s may be a little late for this kind of behavior out of a serious boyfriend. )

Examples of this would be things like baby talk, talk of living together, planning your future together (on more of a basis then 'what should we do next month'), and talk of marriage.

Changes like this, if they happen sudden, can really rattle a guy to his core. Sometimes they may not even be sudden, the guy just didn't see them coming and was taken by surprise. In this context, saying they have to 'figure things out for themselves' or saying that 'they don't know what they need' is basically them just admitting they're not sure if they're ready to continue down the path the relationship is headed.

If you're fortunate enough to be able to talk to them about this more I'd suggest you do so, if its important to you to know why he's being cryptic about his reasons for leaving you. But be warned, the answer you get may not be the most sugar coated of reasons.

I'm trying to understand your question. Are you asking what do guys mean when they say 'we don't know what we wanted' after a break up?
I'll assume that's the question. I haven't personally used that line, but I know couple of guys that have and they used it because from the beginning they knew they were there just for the sex, but they had to give the girl the illusion they wanted a commitment. Once they got bored or found somebody else, it was easier to become distant and say that they needed time to figure things out and weren't sure what they wanted, that things were moving too fast, and that maybe they needed to concentrate on their professional life, etc.
Maybe there are other reasons why, but that's the reason I know as to why some guys say that line.