How He Treats His Friends Tells You Everything
You may not be long-term
If he has no long-term friends, that speaks to his ability to maintain any sort of long-term relationship. Not having long-term friends usually means not being good at things like compromise and forgiveness and generosity. He probably failed in one of those areas with friends in the past and so they dropped off. He will also fail in those areas with you, and you will also leave.