Will you answer questions about love and philosophy?

I am curious as to what people tend to believe when it comes to life partnerships, or even just casual boyfriend or girlfriend situations;

Is it acceptable to you to be in a relationship where you are the second choice? (For example; your SO was and is in love with someone else, but cannot be with that person for some reason or another, and so SO chooses you instead) Why or why not?

Is it acceptable to you to be in a relationship, where the person you are with is the second choice as in the example above? Why or why not?

Is it acceptable to you to be in a relationship where you are loved by your partner, but your partner is not IN love with you? Why or why not?

Is it acceptable to you to be in a relationship where you love your partner but are not IN love with them? Why or why not?

What percentage of people are in these kinds of relationships, and are satisfied with it?