Partner is controlling
Yes, very controlling and abusive.
...but does try hard to be a good partner and is in many ways
He doesn't try, he puts on an act to keep you around. This is what abusers do. He's not good, he's crap.
Pays for everything, does loads round house etc.
He doesn't pay for everything if you work part time and if one person takes on the role of sahm, and the other works outside the home, of course the salary should go into the household. That's a really low bar to set for a "good partner".
Doesn't really like me working although I do part time.
Of course he doesn't like it. It provides you with independence, social contact and enables you to leave him. It interferes with his ability to completely control you.
My issue is that I don't love him and don't like him touching me etc.
That seems very rational, considering what a horrid shit he is.
However my son, who he is strict with adores him.
All small children adore their parents, no matter how bad the parent. It's a primal survival mechanism, like Stockholm Syndrome. Don't put any stock in that, as far as being a gauge of how good a man or Dad he is.
I don't want to ruin my son's life by separating,
You will improve his life and also greatly reduce the chance of him continuing the cycle of abuse in his own future relationships.
I feel I should stay whatever the emotional cost to me.
No. Just no. You have important value beyond just your service to men and children.
My partner is fundamentally a good person, just too controlling for me I think.
Going just by his actual conduct, who he really is, seen in his actions, he's fucking appalling.
He proposed at my 50th birthday party in front of my friends so I had to say yes.
Of course he did. Appalling.
That was 4 years ago and I've just avoided the issue since. I'm just frightened of being alone as my mental health not great and don't want my son impacted...
Your son is better off without an abusive animal in his safe place, his home.
Dad left me a sizeable amount of money
Don't marry this man (or anyone - see a solicitor for advice to protect your inheritance). He'll take your inheritance, abuse you until you are totally broken and then fuck off with your money.
You're stronger than you give yourself credit for, which is why you're here, asking this question and also why you've avoided marrying him. Dump him and fuck what anyone thinks. Your son is more important and YOU are more important. Go and get free.
Save your son, save yourself. 