Or if you mean an audible pause: There may be one but at normal speech speed it is often skipped unless the sentence structure is more complicated than here. However even if there is a pause, it isn’t quite as exaggerated as in the pronunciation by the female voice I hear when clicking above. In any case, the comma is obligatory, as quid_pro_quo said.
Yes, the comma is mandatory.
I made that up, but I do hear the “-ee” suffix used productively on a somewhat frequent basis (albeit usually somewhat tongue-in-cheek) to refer to the passive counterpart of “-er”. I don’t really associate it with any particular accent but I may just not have been paying attention ;)
In German you have to put a comma between almost any kind of composite clauses (the major exception is clauses starting with und or oder). In this case “den du liebst” is a subordinate clause (a relative clause to be exact), so you have to separate it from the rest with commas.
Yes, there are differences between how we use the comma in English (pauses, for example) and in German. I heard that in German the comma is a matter of grammar, while in English it is often to do with style (or something like that, can’t remember exactly, not style but something similar).
I’m not sure how official English grammar views this. I imagine some people will object because this is a restrictive relative clause – a relative clause which identifies the correct individual(s) among a set – rather than a non-restrictive one (one which gives additional information about an already indentified thing). I think there are people who insist that restrictive clauses should always use “that” and non-restrictive ones always “who(m)”. In practice the first part is certainly false, people use “who(m)” for restrictive clauses all the time. I’m just not sure if official grammar condones that.