I am on my second marriage. I first got married when I was 19, which was too young. Now thirty years later my thought on this is that you are choosing someone you can:

1. Trust
2. Genuinely enjoy being with physically, mentally and emotionally
3. I evaluate my partner for their positive and negative characteristics and make an overall judgement on them as a person and if I want to be with them
4. Commit and try not to keep score, though sometimes when things get a bit out of balance that is hard to do

So far second time around is working better with every year :)