✔ 最佳答案
暗戀and單戀的英文都是: unrequited love
you can tell the difference in 2 meanings by the usage. For examples:
暗戀 - Jane loves Roy unrequitedly and Roy doesn't know it at all.
單戀(對方可能知道) - Jane loves Roy unrequitedly and Roy may know about it.
good luck!