Congratulations on the new job! I imagine it must be nice to be working again especially with a great boss.
I understand you are finding it a bit tough and I'm sad to hear you feel like you aren't coping.
Do you mind if I ask what you are finding tough in the new job?
Personally, I've not changed jobs very much but I understand there could be a lot of challenges like needing to learn a lot of new things, getting to know new people, dealing with worry about not being good enough, or even just adapting to a new routine.
It'd be lovely to keep talking to you and hear what you are finding tough.