I'm 29F, boyfriend is 34M. He has an 11-year-old daughter with his ex. He usually only has his daughter three weekends a month during the school year, but his ex is currently on vacation in Japan, so his daughter has been with him for the past two weeks.

The weather has been really warming up where we live and one of my friends opened her pool for the year this weekend. My boyfriend's daughter LOVES swimming. I told her on Thursday that we could go swimming on Saturday and she was ecstatic. Saturday rolls around and she stayed in bed all morning, looking miserable. My boyfriend took her temp and she didn't have a fever. She just told him she "doesn't feel like going anywhere" and asked to be left alone.

It didn't seem like she was sick and she had been so excited about swimming earlier in the week, so I knocked on her door later in the day Saturday to ask her if something happened at school that upset her, or if there is anything going on she wants to talk about. She initially told me no, but she was tearing up. Then she made me promise not to tell her dad, which I agreed to. She told me she had started her period, was in a lot of pain, and was using toilet paper as a makeshift pad. Even with my assurances that starting your period is nothing to be embarrassed about, she still didn't want me to tell her dad.

I ran to the store to get her some different pad options, a heating pad, and some chocolate. As promised, I didn't tell her dad. I just said I was running to the store to grab some snacks for myself and his daughter. His daughter continued to have bad cramps even with the heating pad, so I gave her two Midol tablets. About 90 minutes later she was feeling a lot better. I gave her two additional Midol tablets when she woke up the next morning with cramps.

My boyfriend's ex returned from vacation late in the day on Sunday (yesterday). His daughter had no issues with her mom knowing about her starting her period, and if she had been in town his daughter would have called her. The only reason I got involved is because her mom wasn't there and she didn't want her dad to know. I knew his daughter would tell her mom once she was back, so it was just a day and a half of me helping and not telling my boyfriend. I figured if his daughter's mom thought my boyfriend should know, then her mom should be the one to tell him, as I made a promise to his daughter not to tell.

This morning my boyfriend's ex told my boyfriend what happened, and he called me after speaking to her. He's furious with me for not telling him about what he called a "medical condition" and for giving his daughter OTC medications without his approval. I told him I wanted his daughter to be able to trust me so she will be comfortable coming to me in the future with things that she might be embarrassed to tell her dad about. I also told him that if there was something going on that required medical attention, I absolutely would have told him, but this was just her starting her period. He's still pissed, mainly about me giving her the Midol.

I don't think I'm the AH here, but I also have no kids of my own and am starting to doubt myself because maybe from the perspective of people who are parents I really messed up in this situation.