What's love and what's the difference between love, relationship and a marriage?

I have been thinking a lot about it and finally, I came to a conclusion which is, Being in love is like feeling a sense of pleasure when you are interacting with the person(anything) you are in love with, anyway. Now, it can literally be anything from a pencil to a dog. Now, coming to the relationship, I feel relationships are completely based on needs. Now, it can be the needs of any kind depending on the type of person, like physical needs, emotional needs, social needs, financial needs, etc etc. Coming to marriage, I feel marriage is like legalisation of a relationship on social norms.