Well, yeah, in most cases f and v are the same sound - "f". Except if v is in the middle of a word (which happens very rarely, unless it's compound words, which have infinite variety) in which case it's a normal English "v".

The thing with "liebe" and "lebe" is that, at least in my opinion, the long i and long e sounds that they contain are pronounced somewhat similarly. But are obviously supposed to be different. Except that the mouth makes very similar shapes, at least in the most prominent High German accent (I can't vouch for all the other accents and dialects of Germany, which has the same situation as if you compacted all of the English-speaking world from New Zealand to Boston in, well, a country the size of Germany).

I guess I don't have good news in this area. They just might stay the same to you or with time you might learn to recognize the tiny bit wider that the mouth is opened when pronouncing the long e.