Readers don't get much detail as to how Macbeth and Lady Macbeth drift apart in Shakespeare's Macbeth, we just know that they do. We aren't privy to the workings of their minds concerning their relationship (no dialogue or soliloquies on the subject exist). We just see them not working together anymore.
In fact, drifting may not even be a good word to describe the change in their relationship--it seems pretty immediate.
In Act 2.3 after the two collaborate on Duncan's murder in Act 2.1 and Act 2.2, Macbeth veers from the plan devised by his wife and kills the two grooms who sleep outside of Duncan's chamber. This immediately puts him under suspicion (by at least Macduff) since they are the only two likely witnesses, and causes his wife to faint (because it is so stupid).
Macbeth, apparently, then is determined to make his own decisions. Perhaps he resents the way his wife manipulates him before the killing of Duncan, but that is only speculation.
All we know for sure is that the two no longer collaborate, and Macbeth "wears the pants in the family," to his own detriment, for the rest of the play, planning the murders of Banquo and Fleance and Macduff's family all by himself, all of which lead to his downfall.