Struggling with Mental Health Alone

Would describe myself as an in the moment, “happy”, high spirited, loving, caring friend when in the presence of friends/ coworkers / family. But when I’m alone I just feel lost, broken hearted, confused, dependent on company or substance to stay just okay. I feel like I have to put a smiley face sticker over my face and when people ask how I’m doing I say “fantastic” with a smile and I genuinely am in for the moment with people I’m not entirely close with. It’s been easier to explain my true feelings to my few closest friends and when I’m in their company I’m genuinely happy most of the time. But when they’re not around I just get very low and down on myself although I do what society/family tells me to do to be happy, but at the end of the day when I’m alone sitting awake at night i just feel like a different person craving to be understood. If anyone is in the same boat and has overcame or in the process of overcoming their personal state of low mental health has any advice, I’m open to trying anything at this point and not rely on others/ or substances to feel okay.