Her relationship wasn't taken as seriously as a marriage because It Wasn't One. Its not "so why did it matter that a priest/judge/rabbi/pastor hadn't presided over our union?" Its the fact that they didn't stand up in front of their friends and family and say, "we are going to do everything in our power to stay together through thick and thin until death do us part. We expect there will be sickness and health, better and worse, richer and poorer -- and knowing that, we are going to do everything in our power to STAY TOGETHER because we have made a PUBLIC COMMITMENT to BE TOGETHER. And, we expect your support."
The officiant is just the person who walks you through the ceremony; it doesn't matter who (priest/judge/rabbi/pastor/grocery store clerk) has the microphone, its the PUBLIC COMMITMENT that makes a marriage.
Yes, folks can obviously have committed life long relationships (one of my dearest friends has a live in girlfriend of decades, but they've never publicly tied the knot, and they have legal documents drawn up to give each other 'rights' in the event of sickness/death), but despite their PRIVATE commitment, they aren't married, and that means if they decide to walk away, its going to be "easier" than if they had made their commitment "legal" -- they ARE boyfriend/girlfriend, not husband/wife.
Marriage is a choice. It doesn't make a good relationship bad or a bad relationship good; it is simply two people promising to do their best because they CHOOSE TO BE TOGETHER. Its about taking the "easy out" option OFF the table, and acknowledging the importance of the other person in your life. Its about saying, "this is more than sex, more than like, more than money, more than temporary -- this is who I want to be with for the rest of my life; we are partners in life's journey, wherever it takes us."
The truth is that a bad marriage can literally kill you, while a good marriage can extend your life, so people need to pick their life partners with wisdom; that awesome boyfriend who keeps getting fired probably isn't going to be a good guy to hitch your financial future to, while that cute girlfriend who can't be bothered to go to class in high school because she's spending all of her time on her hair might not have the same priorities about attaining job skills, which again, is a big warning sign about your financial future. I personally know of one couple where the wife financially screwed her husband over WHILE HE WAS IN THE HOSPITAL undergoing life threatening surgery -- he's currently living in a car, while she of little loyalty is shacking up with the new boyfriend.
Marriage doesn't change your character; a slacker, scammer, liar, thief, cheat, fill-in-the-blank is still going to be that same person, while a trustworthy, hardworking, honest, loving, supportive, partner/spouse/best friend is still going to be that as well. Interpersonal conflicts will arise, and if you don't have or learn the skills to resolve them, folks can be miserable until they work through them.
Everyday, marriage is a choice. The fancy dress on the big day isn't "marriage" and the party afterwards doesn't mean a couple will be together in two weeks. Marriage is planning on spending the rest of your life together. What the folks IN that marriage decide that means (where they live, if they have children, how many, how they will be raised, etc.) is between the two of them, and hopefully, both will be happy with where the relationship grows. Legally, there will be benefits acknowledging the "public contract" and also responsibilities.
I believe in marriage, and I believe it should be available to same-sex couples. If only we could convince the idiots to take it seriously when they pick their partners....Sigh.