You said both of you are adults and I think you guys can have ADULT talk with his mother.
Meet her up and talk about this situation that both of you need privacy and will take care of each other.
Let her understand why she shouldn't call that often.
Instead of calling, teach her how to SMS / Whatsapp.

Previously I have a mother who treat me like a baby too.
Especially after I move out, she call me day and night, I know how it feels listening to the same stuff again and again.

Then I bought her a phone and teach her how to whatsapp and sms after telling her that I'm busy with work and my phone's battery drain fast.
You will need a lot a patience for her to learn.
But guess what?
Now she won't call me unless it's an emergency and she don't nag me anymore because she realise that she is talking about the same thing over and over again when she read the chat history.
The best part of all is the sms-es get lesser because she have her whatsapp group =="

She is plainly boring and have nobody to give attention too so I guess you, ADULTS might try my KID way of handling this over obsessed mother.
Can't blame her for giving all her attention to her beloved son
FYI, my mum was divorcee too

It's alright! Forum is open to all comments. That's where we learn from each other If I open a topic and expect only good comments that I can accept .. then I'll be very immature. Of course I don't blame her for loving her son .. but honestly.. we are both working adults and busy at work.. and she would call him during his work. Even though he picks up and say he's busy in a meeting, she would still continue with her long nagging story, not allowing him to put down the phone and it annoys him. And this happens everyday. If he ignores her call, she would be very angry and she would try to call me instead asking where is he (when it's logical that he's working). Sometimes she would even raise her voice at me because her son is ignoring her. Imagine your in-law doing that to you .. breathing down your necks trying to find out your partner's whereabouts .. In fact, imagine your partner doing that to you everyday.. your gf calling you everyday asking where are you? Why you're not home? Nag nag nag, etc etc etc. I thought only crazy girlfriends would do that but not from a mother.

As for moving out of the house, well .. in my opinion he's 32 and i'm 29 .. and it's very much the time to be independent. I don't like to stay with my parents either cause my mother still treats me like a child even at my age ... "My House, My Rule!" concept you know? I realised that when my siblings move out, my mother threats them more and more like than adult instead and it works for me too. But different story from my partner as the mother still wants to pamper him and have him under her wings 24/7.

Nothing wrong with mother wanting to show her love. I highly approve of that! But as to HOW a mother shows it is a different story. To bug us non-stop during our working hours everyday can be frustrating. Partly is my partner's fault for not really talking to her about how he feels. Well .. hope you understand my dilemma ... any opinion is open