The goal of a marriage is not happiness, but unity.
It exists to make you a saint; (and by saint it is by no means tied to any specific religion but to its symbolism of men and women of heroic virtue and kindness) and to transform you into the best version of yourself.
However the best version of yourself does not mean to become more of what we want ourselves to become. It means to become more like God. This means sometimes denying ourselves and choosing what's best for those we love. And that will inevitably lead to suffering.
Therefore, when struggles come, do not be disillusioned that marriage is meant to give you perfect happiness. "Love that cannot suffer is not worth of that name". Discern and remember that nothing worth having comes easy.
There is no one who can give you perfect happiness.