In your body's mind once you've had sex the "relationship" is over. This is especially true for men. They will work like dogs to have sex and then it's over.
All this to say, a relationship needs more elements that are discovered and cultivated before you have sex. It takes time for the mind in your heart and gut to awaken. With this in mind take your time and focus on two things.
1. A relationship is a conversation that doesn't end. 2. A relationship is the ability to make and keep agreements. These two elements will build your foundation.
Let me know how it goes and read A Life Of Love and Dating Advice For Alpha Women in that order.