Is Platonic Hand Holding a Red Flag?

Yes I know, probably a dumb question, but one I wanna ask. So I (22m) recently got broken up with by my ex (23f) after she emotionally cheated on me with my childhood best friend. My ex and I dated for around 8 years now. Right now I’m over two months into the break up, if you wanna know more I’ve posted endlessly on Reddit since the break up.

I’m a fool, over the past maybe half year before my ex left me, she and my old friend whom I’ll call Dick started becoming close friends. I ignored a lot of things, and whenever I confronted my ex she would brush me off and acted like what they were doing wasn’t weird and was perfectly normal. At first I didn’t really mind them getting close, I’d say they were decent friends for a while, and our friend group unfortunately shrank till it was just us three so I didn’t see anything bad. I trusted the both of them because I knew them most of my life. Again, I’m a fool.

The biggest thing that I think marked the beginning of the end was when they started to hold hands. I brought her aside and told her straight out that it made me uncomfortable. That it felt like it violated our relationship. My ex is asexual and is slightly on the spectrum (she’s always speculated it herself, never got it confirmed) so I thought she just didn’t understand what was wrong. However, she then told me about how Dick’s ex told him that he would never hold another woman’s hand again. That Duck was scared that he wouldn’t have that again. Dick’s ex was toxic as fuck so I get it, but their break up happened close to 5 years ago, and it irked me deeply that Dick was opening up to my ex about those things.

My ex also brought up how if Dick was a girl I wouldn’t have a problem with it, and that the hand holding didn’t mean anything. I told her that if Dick was a girl it would still make me uncomfortable, and it confused me why it had to be her to hold her hand. She called me paranoid and said that it was fine, and like a fool I believed her.

Obviously in my case it wasn’t actually normal, but do people normally hold hands platonically? I’ve always seen it as an intimate thing, so am I weird for thinking that? Also if you’re curious, it went from hand holding, to publicly hand holding, to cuddling him, and finally kissing him “only on the forehead” behind my back. My ex would try and hold both of our hands at the same time every now and then, I bit my tongue most times, but when I pulled away and said that made me uncomfortable she got mad at me. I’ve learnt the importance of boundaries unfortunately.