I'm posting for mumsnetter's wise words!
DD is 16, in 6th form and for a year has been going out with a boy in the year below, so still 15. They spent almost all their time together at our house; he had quite controlling parents. His mum always seemed nice but I always felt with the dad their was a lot of anger there, barely repressed at times (eg I took him back a fraction later than they'd said he was to be home once and he was clearly furious and struggling not to shout at me). They always gave the impression they thought they were better than us and apparently frequently told boyfriend that DD was not worthy of him.
He seemed a nice lad but in recent months I became increasingly concerned that he seemed very controlling of DD. She had begun to develop an eating disorder, had lost a huge amount of weight and he seemed to be constantly supervising what she ate.
Last week she confided in me there was a boy in 6th form she liked and she wasn't sure what to do. I said it wasn't fair to be with boyfriend if she had feelings for someone else. She decided she didn't want to see the boyfriend any more - for lots of reasons, not just this new boy. She broke up with him, I thought, as kindly as she could, face to face, but he was clearly very upset. I suggested she let the dust settle but last weekend, in a possibly ill-judged move, she announced relationship with new boy on facebook. However, she seems 100x happier and is eating again.
On Monday, now ex boyfriend apparently saw her in the corridor in school, grabbed her arm very hard, dragged her to the side to ask what was going on with new boy. DD said he was extremely angry and she was quite frightened.
She didn't want me to take any action but tonight she showed the the bruise on her arm and it is really quite nasty, all yellow and faded black. I insisted she photograph it just in case of further trouble but she insists she doesn't want it reported etc.
Do you think I should just leave it? DD is adament she doesn't want it taken any further but I don't think she should accept this behaviour or he should get away with it. But I think if I tell anyone she will not confide in me in future. I'm also worried she might get further trouble with him - there's been no issue since, though.