Do people get partners because as we get older we have less friends?

I think it is quite unfair towards someone to be with them only because otherwise you wouldn't have any friends. Unless of course you both know about that.

Many people do not invest in relationships and that is the main reason they end up alone. I have seen this in other couples a lot.

For example, my father always tagged along but never had any respect for the work my mother put into relationships with friends and families. When they divorced my father became a grumpy and lonely old man who gets increasingly awkward the longer he spends cooped up alone.

He believes his way out is finding another woman. He seems to be unable to understand that it shouldn't be another person's job to "make" his social life...

A partner is no replacement for friends and they can't be the stand in for all other relationships.