If someone is bad in bed, it is always hopeful that the person will get better over time. Having a strong sex life does contribute to a relationship. So, it is important, but it may not be the most important thing in the relationship. It all depends on the couple. Each person values different things in a relationship.
(2) There are ways to improve bedroom behavior. Consulting a sex therapist may help this other person as long as this person is willing to meet with this therapist or counselor and work hard at improving. However, telling your significant other that they are bad in bed or asking if they would want to go to a sex therapist is a difficult thing to do.