OP, your life's meaning shouldn't be derived from another person. You should want to live for your sake, not someone else's!

I'm slightly confused about how your passions and your fiancée interact; do you feel like your relationship is preventing you from getting the personal development and help that you need?

Would you like a career in streaming? Do you feel pushed or swayed towards a different career? If this is your problem, I'd really recommend finding something else to do for money, while streaming on the side. Being self-employed without any guarantee of income and severe depression is very unlikely to work out well for you.

You really need to focus on your own wellbeing for now - do you have a doctor? A counsellor? Antidepressants and talking therapy could make a huge positive difference to your life.