If you want to be happy, you have to recognise that you are responsible for your own wellbeing. You're happiest with your girlfriends, so you are perfectly capable of choosing to do something and identifying that it makes you happy. What else are you doing to make you happy?
It's a bit like posting 'I want cake but I don't have any... why?!'
Have you tried going and getting yourself some cake?
Anxiety is what happens when there is something scary and we're not sure if we have enough support to get through it without being harmed. When we are children, our parents provide that support, so that we are not anxious as children. When we are adults, we mimic their support, and that's how we parent ourselves. That's what adulthood is: it's not the lack of need for parents, it's the ability to parent ourselves. There is still a little kid inside who needs supporting, it's just that we have to do that for ourselves, rather than having a grown up doing it for us.
So, the question really is 'Why don't I have my own back? Why am I not supporting and reassuring myself in a way that relieves my anxiety and makes me feel happy?'
You have a whole, adult person to look after. It's a phenomenal responsibility, and a really busy job. It's not just about making sure they eat, sleep and exercise, it's about looking after their wellbeing, putting them in places where they smile, encouraging them away from places where they don't. Just like you do with your kids.