See, he's a dude. For him, marriage is only a financial liability. Sure you might never divorce him, but if you were to think about it eventually, the outcome would do everything but deter you from it. Not all men are willing to live with a damocles sword above their heads just for a pretty ceremony and rings to wear.

Now, you say this relationship is just practical, but is it a good relationship ? If it works why break it ? Because there's a chance that in the universe the perfect partner exists and that you would miraculously get him ? Cherish what you do have, instead of living in fantasies.