Their daughters end up happily married to the men of their choices. All three unions face varying external conflicts that try to tear them apart, but the love between the couples never wavers.
Wilbur and Edna Turnblad from Hairspray. Wilbur says it all in their song together - "When I need a lift// time brings a gift// Another day with you".
John and Abigail Adams and Thomas and Martha Jefferson from 1776.
John and Abigail have three duets, with "Yours Yours Yours" expressing how much they love and miss each other. Truth in Television, too. Most of the content of those songs was taken from the Adams' actual letters to each other — and John did, indeed, sign multiple letters as "Yours, yours, yours".
Tom misses his wife so much that he has a crippling case of Writer's Block when he's unable to visit her, so Adams has to ask her to come to Philadelphia—where they immediately fall into each other's arms (and then bed).
A few of the vignettes in I Love You, You're Perfect, Now Change have these kind of couples, namely "Whatever Happened To Baby's Parents", "Sex and The Married Couple" and the untitled one featuring the song "Shouldn't I Be Less In Love With You?" It's indicated that the couple in "Wedding Vows" will be this since, despite some initial last minute panicking, they go through with the wedding because they sincerely love each other.
Macbeth: Lord and Lady Macbeth. Yes, they brought doom and damnation upon themselves together, but they loved and supported each other along the way (though Lady Macbeth could get a little mean in her "supporting"...).
Wintergreen and Mary in Of Thee I Sing, who get married in the first act finale and stay resolutely together through the sequel Let 'Em Eat Cake.
It can be taken that Dionysus and Ariadne had this sort of marriage in The Frogs, considering how Dionysus describes their time together: "And the years filled with joy/And my heart filled with pride/Just to know Ariadne was there at my side." And when he's in the Underworld, struggling to figure out who the best playwright to bring back to Earth with him is, Ariadne shows up to comfort him and help him find the answer.
Chris and Ellen in "Miss Saigon". While he clearly loved Kim during the first half of the show, Ellen is the one he wants to build a life with, and she is supportive and accepting of the idea that he has a son by another woman.
Kristina and Karl Oskar in "Kristina from Duvemåla". They even have several songs about it, with lines such as "It is cold and empty// when you've shared everything// and are made to be apart" and "We shall be together when day adds to day// For where you go, I go as well". Karl Oskar also has a song, "Stay", in which he describes how much his wife (who is at that point very ill from scurvy and might not make it through the night) means to him. The musical depicts their initial courtship and early years of marriage, their decision to be the first in their parish to emigrate from Sweden to the US in the mid 1840s, and building a new life for themselves and their six children in Minnesota.