В чём заключается смысловое различие слов relationship и relation? Какое значение придаёт частица ship?

FROM BBC website:

Relationships

A relationship is a close friendship between two people, especially one involving romantic feelings:

They had been together for two years and Mike wanted to carry on, but Jenny felt that their relationship wasn't really going anywhere.

Relationship can be used in two other ways. It can describe two things and the way in which they are connected:

Doctors now believe that there may be some relationship / connection between autism and the MMR vaccine.
It can also describe close ties between people or groups of people and the way they feel and behave towards each other:

The Smiths placed great emphasis on close family relationships and always went on holiday together.

The relationship between the leaders of the two countries has never been closer.

Relations

Relation also describes the link between people, groups or countries and the way they behave towards each other. In this sense there is very little difference between relations and relationship. For instance, we could also say:

Relations between (the leaders of) the two countries have never been closer.
Most of the differences are context specific in this sense. For example, we talk about diplomatic relations and race relations, not diplomatic relationships or race relationships:

Diplomatic relations between the two countries were broken off over this incident and their ambassadors were sent home.

The need to improve race relations in Inner London boroughs is of paramount importance.

Your relations are also members of your family:

I invited all my friends and relations to my twenty-first birthday party.

Mark Totterdale and Simon Totterdale (no relation) are both head teachers in Bristol.

Your blood relations are the people who are related to you by birth, not through marriage. If you say that they are your own flesh and blood, you are emphasizing that they are members of your own family:

He's my own flesh and blood. I can't leave him to fend for himself when he needs my help.

relationship - сексуальная связь
relation - родственная связь

relationship - взаимоотношение, reletion- связь, отногение - первое - более полное, объемное

два разных слова.

Суффикс -ship образует существительные со значением состояния, положения или свойства, например:
friend (друг) - friendship (дружба) , member (член) - membership (членство) .

relationship - совокупная система отношений всех субъектов в отличие от отношения между субъектами

Разницы никакой. Это типа богатство могучего Английского языка.

Грузовой ) плавающий и тп