Guide to Social Activity/Building a relationship
Many treatises have been written, by better and more experienced authors, on the subjects of extracting commitment from another person - even unto a lifelong relationship and lasting dynasty - that is in the long term mutually beneficial. Suffice it to say that, should you be willing to undertake the ordeal, there are many avenues to explore.
That said, building a self-sustaining relationship which will survive through the ages despite the best efforts of third parties and human nature, and without constant vigilance on your part, remains a difficult and unsolved problem.
It is important to recognize that you wish to enter into a form of a contract with another person involving social transactions. You intend to make an agreement to be monogamous, among other things. As is the case with ANY contract, you must first evaluate if the other party is trustworthy/honorable. To be blunt, do not chose a loser/player/bad-boy, with the hope of changing him. A serious mistake in life is to assume you have the ability to change other people; you do not. You can only indirectly influence them to chose to change themselves. Should you chose a loser, and believe you can change him, you will be repeating a common error; you will be setting yourself up for a broken heart.