The Unexpected Turn in My Marriage

I’ve been married to Jack for ten years now. We have a good life, stable jobs, and we enjoy each other’s company most of the time. However, lately I’ve noticed something strange happening within myself; an attraction that didn’t exist before, or at least wasn’t this strong. It’s towards my best friend from college days, Sarah. Sarah is also married to someone else for over five years now, and she has kids. Our friendship has always been platonic, but as time went on, I found myself craving more from her than just conversation and support. A few weeks ago, after a particularly long day at work where Jack was too busy with his own things, Sarah called me out of the blue asking if we could meet up for coffee. The moment I saw her, all rational thoughts went out the window. She looked so different; more mature, yet somehow still youthful and vibrant. We chatted about old times and reminisced over good memories from college, but as our conversation wound down, there was a palpable tension between us that neither of us wanted to address. I found myself wondering what it would be like if we let go of the platonic facade and explored something deeper. I can’t stop thinking about how her touch feels on my skin, or imagining how her lips might taste against mine. This newfound desire has been eating away at me for weeks now, but I’ve been too scared to act on it. What’s confusing is that I still love Jack and value our relationship deeply. There are no hard feelings between us; we get along well and enjoy each other's company in a more relaxed way than with Sarah. Yet this attraction towards my friend seems almost uncontrollable, despite my better judgment telling me otherwise. Is it normal to feel such strong desires for someone outside of your committed relationship? Is there something fundamentally wrong with me that I am feeling this way even though logically I know it’s not right? I desperately need some guidance on how to navigate these feelings and understand why they’ve surfaced now. Any advice or perspectives would be greatly appreciated.