It would definitely be inconvenient, but remember, this is an evolutionarily adapted parasite that "wants" its host to remain alive and healthy (and to avoid making the decision to get the surgery an easy one). The breast growth and lactation therefore can't be too extreme -- so at the high end of normal but not truly debilitating.
Likewise, parasite influence over host behavior is usually very limited to only a few specific behaviors, and even then would only work through hormonal or neurotransmitter signalling (these parasites aren't sentient, after all). Plenty of people with extreme libidos still manage to hold down careers - it can certainly make some aspects of life a lot more challenging, but not unmanageable. Furthermore, that kind of signalling generally isn't subjectively perceived as manipulative, even if the host intellectually knows it is.
Finally, keep in mind that humans are ridiculously adaptable in some ways to all kinds of situations that might seem pretty weird or awful. Especially if the process is a slow one, which it would have to be.
And heck, a parasite that wants its host to stay healthy could probably also engage in other biological manipulative tricks, like tamping down certain kinds of stress responses and maybe boosting the host's immune system, in addition to the abovementioned addictive pleasure. This is adding a bit of speculation to what I'd already dreamt up, but if the parasite has a side-effect of also making the host fitter, healthier, slimmer (albeit bustier), and happier despite the vague body-horror of knowing she "should" feel disgusted but inexplicably doesn't, then the extent to which infestation is an overall detriment could well be debatable.
Again, other than just generally being into breast infestation, a lot of the fun here to me is that the host gets enough out of the infestation and isn't harmed enough by it that she has severely conflicting feelings about how to react.