Super Confused about Office Colleague behaviour

I have worked with a colleague(1 year senior to me) for close to two years, and we are good friends. I generally work with a standing desk(basically you can stand and work, raising the desk). And she often comes to my desk to just chat, this she has been doing in the past as well, and I also go to her desk at times. But over the last 6 months facing something weird. Whenever I am showing something on the screen or discussing something work related on the screen she stands very close such that I can feel her breast on my arms. I get very weirded out. She knows that I am in a long term serious relationship. So I just hope that it's just by mistake, but find it very surprising that she would stand so close and not realise this. Question for girls in this sub, do you think I am reading too much into this and it is unintentional and can happen? And if you think this is intentional, what should I do? I don't know how to handle this, and can't discuss with anyone else either.