I use durex extra thin condoms, and they fit just fine and I haven't had many problems, but when my girlfriend is on top for longer time, the condom starts slipping off, in a way...? Like the base of the condom is still where it should be, but the tip becomes much longer, and sometimes filled with some white fluid (not semen). I'm worried that this could cause problems, in terms of pregnancy risk... Am I right tho think that?
Also, why does a condom behave that way?
This is how Oxbridge students do it.