My ex was an ISFP and the girl I used to like, who I am now friends with is an INFP.
ISFP's explore people, while INFP's explore the world.
It doesn't sound that poetic, but I think it's the truth. ISFP's are very relationship oriented, but never like to commit to one relationship for long. They feel trapped and get miserable. INFP's like to explore the world and experience new things to remain content. The focus is on beauty and wonder in the world. They may change relationships a lot, but that's only because in order to explore, you can't remain stagnant in the world. Their most fulfilling relationships are the ones that accommodate their nature and need to experience the new.