1. DY, I want to preface my responses to your points with the following important point which I think is crucial to an understanding of the whole discussion:
According to the way the OP described his Rav’s response, this does not seem to be a halachic question per se’. It is muttar to drink/eat chalav stam and the Rav whom he asked did not say that it’s assur for him to do so. As far as I can tell, the issue is not “Is he allowed to eat chalav stam?” but “Should he do so?” On the one hand, there’s a hashkafic problem of lessening ones’ standards, and on the other hand, there are his emotional needs. Those are the issues here. This is not a halachic question per se’, but rather a hashkafic issue (as I see it).
2. “You are assuming that his emotional state allows him to be meikil on something he was mekabel on himself. Meiheicha teisi?”
I am not aware of any halacha that says that it’s assur to be meikel on something that you had previously taken on (as long as you do hataras nedarim, if necessary). And the Rav whom he asked did not say that it was assur.