"This is not a friendship; this is a false friendship." False friends are friends when things are going well for you. They are friends when they want something from you -- time, energy, an ear to listen to their problems, help with homework, money. But when you need a friend, the false friend is not there, and always has an excuse as to why it's a bad time, or what you want can't be done, or why he doesn't want to get in the middle of whatever problem you are having.
There isn't necessarily malice in a false friend, like there is in an enemy, but the false friend just can't be bothered. It is not clear from the context whether the OP means enmity or false friendship.
With an enemy, you know what you are to him. It can take quite a while before you understand what you are to a false friend.
I found only low-grade references for this term. But see Fake Friend/Real Friend Psychology Today https://www.psychologytoday.com/blog/the-pragmatic-aspie/201109/fake-friend-real-friend