OK, soooo, fantastic solicitor told me this and gave me the following advice:
Since I've made up my mind, the decision is made, the relationship has irretrievably broken down, things are a lot easier. Agreed. (Bear in mind when I saw last solicitor I hadn't even told P but a lot has changed since then).
So that means:
Step 1 - contact CMS right away. Find out how much the payments would be (I already know this but was too scared to act, unsure when to do it etc.) and first try the amicable route, as always - this is the amount you have to pay now that we are separated. If it's arranged via the agency, they take a fee which would cost X but hopefully we can arrange is amicably between ourselves.
Step 1 is what has shit him up.
Ten minutes later, instead of replying directly to my email, he sent a new one, including the following points:
He's worried about my state of mind (yep, must be who has the problem)
Apparently I agreed to the budget (I was too intimated at first to demand any more initially but after he left, I emailed to tell him many times and in clear terms that it is NOT enough
He was going to take me to a flash location for my birthday this year (its a big one, no guessing please 
)
He looks forward to talking about it when he's back
And signed off with "lots of love" - yes, WTF x 1000.
So I replied several minutes later, please note lovely amazing MNers that I did NOT come on here asking for advice how to respond because I KNEW exactly how instinctively and that is only because of the repeated advice and help from you guys over the past few weeks.
I told him the following:
My mental health is perfect, thank you very much and do no insinuate that there is a problem because there is not
I don't want to go on holiday with you again as we are separated
I never agreed to live this way
But more to the point: are you paying the child maintenance or not?
OK, I a, not fully trained up yet so ahem, need some more advice!!!
Literally a few mins after I started typing this very post, he has replied.
He is still denying that we are separated by saying "we are not separated" and that I have just returned ahead of him and he's happy to "explain this concept further to me when he's home". Really looking forward to seeing him blah blah blah kisses and shit at the end.
I don't have any choice but go straight to the CMS, do I (or in my case another organisation that enforces it if they live abroad - I have checked BTW and his country is covered THANK FUCK)?
Interesting when I was given this advice from a WA woman I spoke to, way before I had decided