Does HASHEM forgive repeated sins or sins that have already been repented for?
H-shem does forgive sins that the person did repeatedly, (unfortunately almost everyone as certain avreiros that they have done repeatedly). However it is harder to do teshuva for such a sin. The reason being is that after a person repeats a sin he loses is sensitivity to feeling bad for the negative act, and also because he got used to doing he aveiro. Secondly, because the negative act became more of a part of him, and therefore the person has more to uproot of the negative act to uproot. Rabeinu Yohan in Sharei Teshuva 1-11 talks about this and he says that when someone got used to doing an aveiro, the first step he should take is to distance himself from doing the sin. Then afterwards he will be able to feel remorse for the action.
Regarding sins that a person already repented for and he fell a second time, H-shem is a merciful king and He will forgive a second time and a third time too also, (as long as we don’t say, “I can sin now because I will repent afterwards”, and even then it is possible to do teshuva, however it will be harder). In fact it is a verse in Mishlei, (24-16) “Sheva Yipol Tzaddik V’kom” a tzaddik can fall even seven, (or more) times, but he gets up and does teshuva for his sin, and he continues to climb higher. H-shem knows that we are humans, and that we make mistakes, and he also knows that we can make mistakes even more than once. Therefore he will forgive us as many times as we are willing to repent, as long as we mean it seriously.