He's agreed to see a therapist after we had a chat a couple weeks ago.
Has he taken any steps towards this - shortlisting therapists/ calling for an appointment/ talking to his GP and getting a referral?
If yes then he may genuinely just be insecure and bringing previous emotional trauma into your marriage. In which case he would do whatever it takes to ensure the marriage he values remains one where you want to stay.
If he's not lifted a finger to find a therapist yet, then he has no intention of doing so, so I think you may have a common garden-variety controlling man on your hands who is looking to control and monitor every aspect of your life and dressing it up as insecurity on his part.
So which is it?
Insecurity is the most effective way of controlling someone because it feels like something that could be easily helped by a quick check-in message halfway through the night out. A little thing that reassures the partner you love, right. He just cares you got to your destination ok. Because he loves you. No harm. Right?
But it then becomes insidious. Like asking you to add the find my phone app to your phone, because the last time you didn't text him, he was worried. Or reading your messages, just for reassurance. Or face-timing when you are out with friends because he wants to see exactly where you are misses you.
And then it very slowly progresses to scrutinising what you are wearing, changing what you wear, why you put make-up on, or why you booked a hairdresser or a wax appointment, or bought a new dress. Why are you getting all dolled up going to work. And why the red knickers. Who are you fucking at work? You must be if you put on those because they are red. And have a bit of lace on them.
Gradually you'll phase out friends because your DP is insecure about your best friend's husband, or your sisters husband, or if you won't do it, he'll create a scene or a row which ensures that those people will draw away from you both.
It won't be enough to monitor your friends, your phone, he'll need to see your bank accounts as well. In fact, just let him control those altogether because you can't be trusted with financial matters because remember you went and bought underwear in M&S that time, and you were just restocking your knicker drawer and you wouldn't have told him only for he found the receipt in the bin. So you must have bought them to wear for an affair.
Or you'll agree to start a family, have a few kids then he'll make it difficult for you to return to work, so you are more reliant on him in every way. So even if you wanted to leave, you've got nowhere to go and no money to go.
That's how it starts, and how it progresses with a controlling man.
I very much hope that you do have someone who IS fixable and will undergo therapy and that it will work, but because the alternative is a miserable existance for you and any kids you'd have.