Although this is addressed to married couples, I think it applies to those super-close, David/Jonathan friendships in life as well.

Thirteen Decisions that Help a Couple Become Intimate Companions
• I will lock the escape hatch and throw away the key
• I will be intentional
• I will make our relationship a priority
• I will revisit my expectations
• I will champion you
• I will nurture my private life
• I will be responsible and reliable
• I will be honest
• I will connect with you
• I will reveal myself to you
• I will allow you to influence me
• I will work through issues with you
• I will forgive