Though the spontaneity that you two generate together is probably be a big part of what attracted you to this person in the beginning, ultimately, you might find your partner too unpredictable to really feel like this relationship is a safe bet. You don't know where the relationship is going or if you can really trust the bond you share -- heck, you aren't even able to trust this person to show up when they say they will! After a while this will start to wear on you.
In some way, you are on two different pages. You'll wish you could settle down a little more together; you'll be willing to trade in some excitement for some stability. Unfortunately your partner won't want to make that trade; emotional ups and downs really rev their engine, and without them, the relationship would seem boring and hardly worth the trouble. If you start to notice that your lover constantly seems to be running away or keeping things from getting too serious, you might need to sit down together and have a heart to heart about where each of you sees the relationship going. If it's to work out long-term, it will inevitably mean that you, as the partner who wants more security, are going to have to compromise your emotional needs and ultimately settle for less than what you would have hoped for. Don't let the choice be made for you; talk it out and make your decision consciously, together.