By Stan Tatkin // If you’re in a long-term relationship or want to be in one, I can give you straight-up advice on what to do right now to safeguard your relationship from avoidable trouble. First, let me explain why you should listen. As social animals, we depend on each other for survival on many levels: physically, psychologically, emotionally. In the wild, primates procreate and pair bond, on average, for four years: sufficient time to raise one child and protect it from the hostile environment. Nature cares not about long-term relationships. Most of us modern humans, however, do care because we are part of a society that values, even requires, cooperation, collaboration, and social fidelity to agreed-upon principles of governance. We also live a lot longer than either non-human primates or our recent ancestors. All this suggests the value of taking active steps to ensure the longevity of our relationships. Now, that’s not always easy. Romantic love waxes and wanes over time. Mutual physical attraction can dim as our bodies undergo slow but inevitable changes …