I guess I have no idea what the connection is with her "friend" and her boyfriend and why having a boyfriend will cost her a friend but I have a sneaking suspicion that she will grow distant from her friend and eventually break up with this guy and that will fuel enough heart break for 3 more records.
In my opinion, Taylor Swift is a truly warm and kind person who would be friends with the entire world if she could. Taylor's friendship with Ed Sheeran seems to be a genuine and solid one with plenty of room for romantic interests outside of it. Both parties are mature enough to sustain mutiple relationships seamlessly.
Taylor Swift's new relationship with Calvin Harris is not going to effect her friendship with Ed Sheeran in any way. Swift and Sheeran, who performed on Swift's tour together recently, have only ever been close friends. Swift, Sheeran and Harris are all friends, and just because two of them are dating does not mean that relationships are going to be strained.
I think Ed would be a bit more mature and will still be able to hold a relationship, platonic or otherwise, with Taylor. Many people still continue to have friendships with people of the opposite sex while in serious, committed relationships. I think Ed and Taylor will still be friends.