9 Of the most common reasons that couples in a long-term relationship break up

Unlike all the other creatures in the animal kingdom, human beings have a somewhat complicated life cycle. For us, finding a mate is not as simple as just latching onto the nearest person and hoping to procreate - we have to woo our intended partner, and really form a proper relationship before we get into starting a family or agreeing on a lifelong companionship.

However, more often than not, the efforts we put into building a bond with another person get laid to waste, and the years of dates, romance, and shared experiences end up fizzling away into nothing (or sometimes a nice friendship, if you're lucky).

But how can you tell if the person you're with is going to ditch at some point down the line? Or even if you, yourself, might get tired of the relationship? Well, here's the nine most common reasons that partnerships end up breaking down - so watch out for them if you can...

1. Sex

While it's not the be-all and end-all of a relationship, sex is sort of like the icing on the cake. Unfortunately, if some people don't have enough icing, they tend to get bored of eating plain old sponge - and so they decide they want to eat elsewhere. Basically, if you and your partner don't have the same idea on how much nookie is enough, it could spell the end of the relationship.

2. Money

One important part of being in a relationship is learning to share. This means dedicating enough of your time to someone, splitting your space with them, and, more seriously, ensuring that the both of you are handling money in a fair way. So, if one of you starts spending more than their fair share - or if one person is very controlling over the joint funds - that can drive a huge wedge between the two of you.

3. Communication

We probably should have worked out by now that people aren't mindreaders, and yet we treat them as if they are every single day. If you're not happy about something, you need to tell your partner. If you are happy about something, it's helpful to share that with them, too. As soon as you stop doing that, the foundations of the relationship will start to slip away, and you'll just be two people who don't talk anymore.

4. Kids

Sometimes, having kids adds a burden that the parents simply weren't expecting - and sometimes the opposite happens. Older couples with adult children often find that their offspring were the only things keeping them together all that time, and "empty nest syndrome" urges them to go their separate ways. Either way, the dynamic that children have in a relationship often changes the way their parents feel about one another, and sometimes not for the better.

5. Stubbornness

As relationships and people age, they change. Unless they don't. Sometimes, people get stuck in their old ways and refuse to compromise for their partner - and it gets tiresome after a while. We're not saying you should change for someone else by any means, but if you have some bad habits that irritate your partner, be wary that they could become a dealbreaker in future.

6. Cheating

This is a huge factor that often comes about as a result of several of the other items on this list. While the reasons that people cheat are always fairly murky, the fact is that a relationship is very difficult to recover once one or both partners has committed some form of infidelity.

7. Life changes

Getting a new job, suffering a loss in the family, or even moving to a new location are just a few huge changes that can cause a person to undergo certain personality alterations. And as soon as one person begins to behave differently, the whole dynamic of the relationship shifts, and that can eventually lead to it falling apart.

8. Selfishness

If you want to spend your life with someone else, you really can't go about it in a selfish way. This means that you need to entertain your partner's needs as well as your own. Can't do that? Well, it's going to get old after a while - and nobody wants to spend their life with someone who can't be bothered to make them happy.

9. Health

Unfortunately, even in the strongest of relationships, personal health can interfere in a major way. Mental health issues, in particular, are often very difficult to communicate, and can leave both people feeling frustrated a lot of the time.

As you can see, most of these factors are controllable - and, for those that aren't, they can almost always be worked on with enough cooperation from both sides. Unfortunately, though, some partnerships just aren't meant to be.