Emotional promiscuity is kind of like dating a lot of different people and not really committing to just one. But instead of dating, it's about sharing your feelings and emotions with lots of different people without really choosing who you want to share them with the most.
You know how you have your best friends and your other friends, and you tell different things to different friends because you trust them and feel close to them? Emotional promiscuity is when you don't really have a best friend or anyone close to you, so you tell lots of different people all of your feelings and don't really keep anything special or personal for just one person.
It can feel good to have lots of people to talk to and share your emotions with, but sometimes it's important to have one or a few close friends that you trust the most and share your deepest feelings with. It's kind of like having one special toy that you keep with you all the time and love the most, even though you still play with other toys sometimes too.