Forever is overrated?

While watching TV today, I came across a product (I don't remember what it was) whose tag line was 'Forever is overrated!'. That set me thinking - Is it or is it not?
At such a young (is 23 young??!!) age, I really don't know the answer to the question.
I feel it is! I guess it is difficult for a person to spend the rest of his/her life with another person without ever surrendering to temptation. There must be instances when your fidelity gives in, when you end up cheating on your spouse even when you don't want to, when you succumb to the gratification of your senses.
There are so many people who say that marriage as an institution is failing. 'They lived happily ever after...' is just a phrase that is used in the last scene of movies or in the last paragraph of books.
On the other hand, I also think that there is nothing as beautiful as monogamy. The amount of courage and determination required to reject a one-night stand is only reflective of the love that a couple shares. But today, how many people actually remain faithful to their spouses? How many people have never had a fling after their wedding? Can I say with complete surety that my dad has never ever slept with another woman after his marriage? I can vouch for my mom, but I can't for my dad.
Anyhow, I do feel in today's world, when people are becoming more confident, bold and beautiful, forever is a concept that is losing relevance. I might be wrong, but only time can tell.