Edited -- Thank you all for the helpful comments.
Can an avowed non-Jewish atheist pour my non-mevushal wine for me? Can I share a bottle of wine with him/her?
Shulchan Aruch YD 124:6 states that any non-Jew, even if they do not serve Avodah Zarah, makes any non-Mevushal wine that they produce, touch (and pour) prohibited to drink, although not prohibited to benefit from:
כל עובד כוכבים שאינו עובד עבודת כוכבים, יינו אסור בשתיה ומותר בהנאה; ומגען ביין שלנו, שוה ליינם, שאסור בשתייה.
The Taz explains that this is due to the Issur of Benoseihem, namely, an issur due to being "friendly" with a non-Jews, in that it may lead to intermarriage.
Therefore, you may not have an atheist pour you non-Mevushal wine.
The same Pesak is given in this article. Many Poskim apply this logic to Muslims as well, since they do not serve Avodah Zarah, See Shu"t Yabia Omer 7:YD:12.