The relationship effect.
When I am in the relationship, it feels good to have someone when you come back. she smiles and hugs you. it is also very convenient that someone helps you with so many things. If there is a social need relationship fills it perfectly. If you are alone you might feel lonely and at unease and a thought of doing this for the rest of your life could be painful.
A relationship puts some demand on you, it is not as simple to just come to the cafe and work, that can be taken personally by her. It also comes with the whole package. there are conflicts and compromises. A relationship moving forward may even include family and other responsibilities.
Then there are mutual things like sex, where my preference is affecting her.