My reasons for suspecting him, is he comes home from work (definately after at the least drinking) but he paces the house, rants
Where is he drinking in lockdown? At work as well? This behaviour above on its own is unacceptable - it’s domestic violence / emotional abuse. If your child is seeing, hearing or sensing this this will be having a detrimental impact on their emotional development. Children absorb and internalise abuse and stress - they don’t understand it, it causes fear and confusion and they develop anxious behaviours that by the time their are teenagers become chronic MH issues. Your child will also be sensitive and absorbing your stress and preoccupation and will feel unsafe.
If your partner wants to get clean - they should leave the home and get on with it - you and your child do not need to endure his withdrawal or live the roller coaster ride of recovery.
He has repeatedly lied to you, gaslighted you and is burning through family money. If he is spending £400 on coke and unable to save to pay for his half or a family holiday - who do you and your child go with? Or will you pay for him?
Regarding your inheritance and your other accounts - change your pins and hide your cards - keep a v close eye on your accounts. He will also feel entitled to that inheritance - because cokeheads are arrogant, entitled and driven.
What are his plans for when he fucks up at work or gets caught and loses his job - does he have a cash contingency to see him through to the next job? Or will you be bailing that one?
As PP said it’s not just the financial drain but the emotional battering that you and your child will endure. And it gets worse, it’s a progressive disease - they need more and more just to get through the day. And that costs.