Relationships take work, that's a given. But why put in all that hard work if there isn't a future for you guys? When you know, you know..
You can spend a lot of time together and not drive each other to the brink of insanity. It can be quite testing to spend a lot of time with each other and I feel that this is a key indicator as to whether you can spend your lives together. Do you argue all the time after you've been around each other too much? Of course, everybody needs their space, but if you find it difficult to spend long periods of time with your man without wanting to kill him, chances are he's not the one.
You can see past his bad habits. Will you get sick of his farting in bed? Will the smell of his feet become totally unbearable in 10 years time? When you find the person you are willing to commit your life to, you will see past their nasty feet picking and peeing on the toilet seat because you love them, and it's not enough to put you off.
He's your best friend. I'm not implying that you should spend evenings painting each other's nails and watching Gossip Girl but he should be the first person you want to share any news with. When you have a really good day, or a really crappy day, he's the one you want to share it with. You're a team.
You've got each other's backs. When Jackie from work starts being an arsehole, he listens to you rant for hours about how horrid she is and agrees with you although he's probably never even met Jackie. If you don't like her, he doesn't like her.
Your family and friends approve. A lot of people don't realise how important this is and have the attitude that it doesn't matter what everyone else thinks because you love each other. However, it can be seriously testing if you can't get on with each other's families or his friends want him to be a single jäger-drinking machine every weekend. This really can put strain on a relationship.
There isn't really anything massive to argue about. Of course you bicker and have days when you annoy the hell out of each other but really there are no major problems and you always forgive each other quickly after a little spat.
Trust. The simple fact is that if you don't trust each other 100% there is absolutely no point in your relationship and it's not going to work.