Do you really need this explained to you? Stubborn people will wear on one's nerves, because they never give in. If you love someone than you sometimes have to compromise for them. Stubborn people don't do that, which can make the person that lives them feel unimportant.
Because it's their way or the highway.
The key word, "stubborn" They won't cooperate. Is the problem that they don't love you back?
I don't know.
Because someone who is not willing to 'give' is emotionally draining. Being chronically stubborn is being 'controlling' .. Granted, we all can be a little stubborn when we are convinced we are right about something..but, there are people who would NEVER accept that they are incorrect or misinformed about something because they associate being 'wrong' with weakness and 'not being in control' ... And for some people with narcissistic tendencies, that is just unacceptable.
Stubborn ain't so bad. It's actually one of those words that has an irregular conjugation:
I am stubborn; you are obstinate; he is a pig-headed fool