How long can a marriage last? Some of us have a delightfully happy marriage (you're blessed), some have a rocky one, while others have ended theirs. When a marriage fails, the blame falls on incompatibility. Maybe, but that's not always true and that's not the main reason. Personally, if you want your marriage to work, you need to have a really good relationship with your partner from Day 1. You need to work hard.
If you expect your spouse or partner to be there for you all the time, but you do not reciprocate, then your relationship with them will go downhill real quick. Men often believe that when they're into a relationship, all attention must go to them; well, if you have that kind of mentality, it's time to change because in a relationship, you'll need two hands to clap, and these hands have to continue clapping till the end of time. To be fair, it goes the same way with women too.
If you assume that life is so simple that you could just let your partner go any time you don't need them or when you're sick of them, then you're sadly wrong, too. It takes a long time to build a relationship. An everlasting relationship constitutes a continuous act of getting to know each other - it just doesn't stop when you're married - it goes on. Therefore, don't just let a fish go if you believe it is very precious to you just because there are tonnes of other fishes in the ocean that you could choose from. It is sometimes the ugly fish that could sometimes give you the best taste (but it depends on how you cook it, too).
Don't you ever believe that if you want to have a successful relationship, both need to have some common interests. Well, in my personal point of view, that's a biased statement. Two people can have many opposing opinions, likes and dislikes, and attitudes yet get along very well till all eternity. For instance, you could be a doctor, and your partner could be an administrative clerk. If you could just let go of your status-consciousness and egoism, and focus on building your communication and relationship instead, then sparks will fly. There are also sacrifices to be made - and both parties need to do that. If either one is egoistic and chauvinistic all the time, then the relationship will eventually crumble.
And yes, some people are just not meant to be with each other. I can't deny that. No matter how hard you both try, there's simply no chemistry. Then, the relationship has to be platonic.