For what follows, let us understand by the term "libertarian" someone that believes that any choice freely made should be permissible, provided only that that choice does not result in direct harm to someone else. I say "direct" harm so as to exclude cases such as morally damaging someone else by one's poor example, or acting in such a way as to deny the benefits of one's own presence to others (say, by choosing to go away from someone). By contrast, let us understand by the term "liberal" someone that believes that choice and freedom to choose should be maximised, provided that such choices do not result in direct harm to others. (This is a different use of the term "liberal" from my normal use, and isn't precisely what I believe in personally when I describe myself as a "political liberal", but it will suit our purposes here.)
Now, it is of interest to understand what is the difference between believing that any choice freely made should be permissible, and seeking to maximise choice and freedom to choose, for as we shall see the difference between these things is important in a number of current policy debates.
An important case that allows us to see how the beliefs of the libertarian and the liberal (as defined here) differ is this: the libertarian will believe that I ought to be able to choose freely to sell myself into slavery. The liberal will not.
Why does the liberal believe this should be forbidden? Because if I sell myself into slavery, then my choices thereafter are constrained and curtailed - I have less freedom than if I had not sold myself into slavery. So by denying me this one choice, we would increase the totality of choice and freedom to choose, over time. (Of course, others - such as authoritarians - might object to permitting slavery on other grounds - what marks out the liberal is that it is this argument that is really crucial.)
You think this an odd and irrelevant case? But here is that same case: the libertarian believes that I ought to be permitted to choose freely to take a substance (say, a drug) to which I will become totally addicted, enslaved. For the libertarian, it just doesn't matter whether a drug is addictive to the question of whether it should be legal. If your argument that some drug or other to be legalised depends on you offering (usually very poorly-evidenced) claims that that drug is not addictive, then you are not a libertarian - you are a liberal. For the liberal believes that if a substance is sufficiently addictive that taking it is liable (for a sufficiently large body of takers) to result in dependence, and if such dependence matters (say, because the drug is very unhealthy), then its use should be forbidden, because permitting its use will result in less choice and less freedom to choose, over time.
Here's another case. A libertarian will believe that anyone ought to be permitted to kill herself, even if that choice is made in a moment of weakness. The liberal will not, because permitting such a choice now curtails the suicide's choices later.
One last one. A libertarian will contend that absolutely any rate of interest or other return-generating contract should be permitted as an obligation on a borrower, provided that that borrower enters freely into the contract with adequate knowledge. The liberal may be able to imagine that some such contract would so constrain the borrower thereafter that entering into it - even freely - should not be permitted.
Which better describes you - liberal or libertarian?