If you have no good, friendship feelings for someone, it's better to let them go. Even though your friend values what little relationship you have, it would be a service to her to let her go and form real friendships with someone who wants to spend time with her.
Thank you SHelley, deep down my heart i knew this of course. I don't have the idea that I hold her back to get involved with other people.
Another reason for ending this friendship, would be that her boyfriend is extremely jealous. He thinks I want to take her away from him, which has never been my intention. I don't have those feelings for her at all.
Thanks for your great advice,
Jo