I think you know you're being emotionally supported when someone actively listens to your problems and seeks to comfort you when you are going through a rough patch. Someone who you feel comfortable telling about your emotional health who also seeks to give you guidance if asked, someone who knows your triggers and actively works to help you recover from or avoid being triggered all together. For example, I have a close friend who I know I can cry with, someone who i am honest with about my emotional/mental state who has told me I can I can crash on their couch when I'm extra lonely and need to be around people. Sure I feel needy when I rely on them but I also know i won't do anything I regret when I'm with them.