A day to myself, when the sun shines and friends are available, is rare. I wake happy and smile through breakfast, when R comes to look after the children. We drink coffee in the kitchen and I notice a bruise on his forearm the size and colour of a ripe fig. It's nothing serious, but I want to ask how it happened. I resist, however, certain that any answer will set my mind racing into all sorts of danger. Instead, I tell him he looks well, because he does: handsome, glowing and, alas, still charming. I want him so much.

In the past week, my main focus has been the children, and now I have time without responsibility I want to relish the freedom that a day away from parental duty can bring.

Something as innocuous and insignificant as the bruise could, in more unsettled times, have had the potential to ruin a perfectly wonderful day. I would have taken that bruise and made it the focal point of a fabricated story with many outcomes, my imagination reigniting dark scenes from previous times with R.

The bruise could have been the result of a drunken fall, a one-night stand or, more pertinently, something that was absolutely nothing to do with me. There's no doubt that I would have given the story an ugly ending: confronted R with my made-up tale and prodded him for answers, then apologised in a shameful attempt to put out the fire my demented attempts at guessing had created. The furnace would burn all day and ruin any good feeling.

The bruise is probably the result of no more than a knock against a doorframe. I question my sanity when I think about how my mind can work.

Obsession is a word often used lightly, as in "I'm obsessed with Breaking Bad" or "I used to be obsessed with white chocolate but now I prefer dark."

"I'm obsessed with what my husband's doing and I'm not paying much attention to anything else that's going on," was something I would have been loth to admit, but until recently it was true. R was on my mind all of the time; he was my main obsession.

Then there were the offshoots, the branches from the main trunk that occupied most other parts of my brain: other people – people getting it right. If R and I were doing it wrong then I had a habit of fixating on those who seemed to be so much better at relationships than us. I became obsessed with wanting to be like them.

I would watch other couples with the curiosity of a spy (but smiling at the same time so as not to look too mad or sinister). If, for example, R and I went out to dinner, I would listen to others' plans: family trips or mundane household tasks. I wanted to experience the normality other couples had. I craved security, desired the whole-hearted commitment that appeared to exist in loving relationships, despite ups and downs.

I examined other people's relationships in much the same way that I used to compare my adolescent, chubby body with the pin-thinness of runway models: with flawed eyes and a warped sense of perspective.

I wanted to be someone else. I wanted R to be someone else, too, for a time. I blamed the alcohol for everything. It was the reason that R and I weren't a happy couple for a long time before we separated. If the children were ill or badly behaved, or the car broke down, or the cat was sick, or the taxman landed me with a colossal bill, it was alcohol.

I could have drawn a line from any incident and bent it in all the right places so that it pointed directly at R, and his drinking. Blaming is quick and easy. "If you didn't drink, then we could be happy," I said, smug, blameless and oblivious to the damage I was doing.

But now I can't point my finger at the alcoholic, because he is not living here any more. I can obsess but it is pointless. I can compare, but it will only make me feel like I'm not good, strong or clever enough to be OK. So I'm not allowing myself to blame, fabricate or imagine things that have nihilistic endings, for now.

The days that start well will often end well if I smooth down my spikes and take responsibility for my behaviour. Once I forget about the bruise, I am away, enjoying myself. I feel like one of the happy women I have often envied in the past. Like the bruise, the feelings of anger, anxiety, resentment and shame are already fading.