In Shakespeare's Macbeth, the relationship between Macbeth and Lady Macbeth seems to deteriorate as the play moves along. In fact, the cooling of the relationship probably begins soon after they work together to assassinate King Duncan, when Macbeth veers from his wife's plan and takes it upon himself to kill the two grooms. This raises suspicion concerning Macbeth's role in the assassination, and was not part of the plan.
Lady Macbeth faints soon after she hears the news that Macbeth has killed the grooms. While it is possible she's faking in an attempt to take the spotlight off of her husband, it's probably more likely the fainting is real, and is the result of her being shocked by Macbeth's stupidity (see Act 2.2).
From then on, Macbeth acts without consulting his wife: we barely see her the rest of the play (and when we do she's either trying to calm down and control the uncontrollable Macbeth, or sleepwalking and apparently suffering from major depression). As Macbeth takes full control mistake after mistake is made. The tragic ending is the result.
Notably, Macbeth's famous reaction to the news that his wife is dead--the "Tomorrow" speech--is not mainly about his personal loss. He slips into nihilism because his wife's life (the same as his) leads to nothing. He laments the uselessness of her life, his life, and life in general. His speech is not really personal, but philosophical (see Act 5.5).
I'll let you decide what exactly that says about his marriage at the time of his wife's death.
Everyone begins to dislike him. He is a disgrace to the people of Scottland. because of all the guilt his wife has gone psycho and is unable to deal with the stress and commits suicide.
A saying goes thus: "As you sow, so you reap." Another familiar proverb is "One who digs hole for others, falls in it himself". Macbeth faces almost a similar sort of consequence. By killing others to make his path clear, Macbeth tries to achieve his goal. But, at the end, through his tragic death along with his wife's pathetic disaster, he becomes disillusioned and is doomed to a terrible end. That's why he realises at the end that life is nothing but a "walking shadow".
Not his life alone faces tragic conclusion. Lady Macbeth becomes insane and her lunacy results in suicide. The courageous woman turns to a vulnerable, lunatic creature. Destiny's turn-taking makes her a complete contrasting character at the end.
Macbeth's ambition, instigated by the witches' equivocation, reaches an extreme stature. His wife, too, gets over-confident. This Icarus-like nature destroys both of them. In fact, assassinations of many dignified people could not save them from disaster. the effect was so awful that Lady Macbeth loses her sanity. Thus, their happy marital life results in an unhappy ending, where dead Macbeth is named butcher and his wife fiend.
So, finally, Macbeth and his wife face a tragic downfall because of their own deeds.