The children and I are back from our holidays. R comes to see them for a few hours at the house, and I go out. When I return, chaos rules. "I have to run. I'm exhausted and want to sleep, but I'll come and see the kids tomorrow if that's cool?" R says.

Home for him now is a studio flat around the corner.

"Bye then," I say, wanting him to tell me he is lonely so I can ask if he would like to stay for dinner. I wonder if I will ever know what is going on in his life. It was hard when we were together, but I feel as if he has become a wholly elusive figure to me now.

As R closes the front door behind him, I remember that he has left a bag of his clothes in the hall. I grab it and walk out on to the street, looking left and right. I spot the back of him as he heads in the opposite direction from his flat. "You forgot this," I shout. He picks up his step without looking back, and I continue after him. He hails a bus on the way down the hill, sprinting to catch it at the stop.

It is bizarre, almost farcical, because it appears that he is running away from me. I feel like an idiot, a fishwife, a stalker. He steps on the bus, a smaller figure now in the distance, and I turn to walk the few steps home.

I want to text him and ask where he was going in such a hurry. When we were together and he was drinking, he lied all the time. Now we're not together, I can't really ask him the things that I want to know, because it's not any of my business.

My couple of weeks away from R taught me that I could feel content without him, but now I'm back I have to deal with the fact that we will see each other regularly because of the children. I fear that I'll start obsessing about everything that he is doing once more.

My first thoughts when I saw him after our break: why do you look so happy? Are you enjoying your freedom? Who have you been having energetic sex with? How much did you drink last night? And more pressingly, why do I still care?

All of these erratic thoughts make me angry, upset and, most of all, resentful. I wanted him to feel worse than this. I want him to fall harder than I have, even though I instigated the split.

Carrie Fisher once said: "Resentment is like drinking poison and waiting for the other person to die." Her words couldn't be more succinct in summing up how I feel at the moment. I am fixating on R's eventual fall from grace (will he slip off the wagon enough to lose his job/hurt himself badly/disappoint the children once again?) and my bitter thoughts are turning me sour. If R's not doing so well, I'm doing worse.

At the moment, I have forgotten everything I learned about detaching with love. Instead, I am clinging on with hate.

When I feel like this, I need listen to the people who have helped me in the past. I'm sending random angry missiles in R's direction, but there have to be some boundaries if the vitriol is going to be at all helpful in exorcising the pain.

I must realise that I can't control R any more: I can't be the private investigator, worrying about his mishaps, or with whom he has been sleeping, or how much he drinks or takes drugs. These are just not my problems, and I must be strong and brave enough to let go, or I will only have myself to blame.

R's not doing anything differently – he is drinking and denying it, but he has always done that. And now, here I am, single, healthy and able to make the changes; I realise how crazy I am wasting time and energy in willing R to do the same. Sadly, in my disillusioned state I often believe that R will change when he sees what he has lost.

But just like the "one last drink" that he is probably having right now before he gives up, I write one last text before I give up on splenetic dialogue with R.

"I hate you."

I hate myself for being so childish, so I delete it without sending. I realise it is time to get back to my support meetings, because R's not the only one who needs help.