Relationship Advice. In this situation?

Hi, I have been dating someone in a LDR for a year now and I am quite serious about her. I have no major complaints from my love life but the only thing that bothers me is that her ex is her best friend. They chat & have phone calls almost everyday. She works far from her home & her best friend is from her native city so they don't hangout everyday but whenever she visits her home they hang out everyday. She spends most of her time with him than what she does with her own family. I understand people staying in touch with their ex-partners but this much? They had a serious relationship that lasted for 4 years and were almost about to get married but then they broke up because she never felt romantically for him & eventually fell in love with me. I have tried talking to her several times on this topic and set limits too. Once I asked her to choose either of us to which she said she can't & can never do that. She has been always honest with me but what should I do in this situation?