I'm currently navigating a challenging situation at my job where I genuinely enjoy my role, but I'm facing difficulties with a colleague who acts like my lead, even though she's not officially in that position. We share the workload, and her mood swings create a stressful environment. Some weeks, she's incredibly supportive and kind, but during busy times, she becomes cold and dismissive, which has started to take a toll on my mental health. I've found myself crying in the washroom just to cope. Recently, I discovered an internal position that I'm really excited about, which would be a step up in both responsibility and pay. The hiring manager and team have encouraged me to apply, and my current manager and HR suggested I talk to this colleague before submitting my application to maintain transparency. However, I'm worried that if I do, she might take it personally and make my work life even more difficult. If I choose not to inform her, I fear I might be going against expectations, but if I do and it turns sour, I could end up in a worse situation if I don't get the new role. I'm stuck between staying in a role I enjoy but in a stressful environment or taking a risk that could benefit my career and mental health.