Love is the one thing that cannot be explained. Not even science can explain it either.
Relationships can be platonic, but I believe when people idealize a platonic relationship when they haven't found The One yet, they'll end up having sex more often than planned with The One. Not saying all, just saying it's a possibility. You can have a platonic relationship and only have sex when you want children. I believe that's the kind of relationship my Christian aunt and uncle has. They gave birth to two children and I had never heard them have sex on the regular. In my opinion, I don't know how they did it. Though at the end of the day, everyone's different.
Acting on impulse is one of the obvious signs of love. That can be friendship love, or romantic love. Being impulsive plays a part in both.