Trying to understand coworkers behavior?

So I (26M) and my coworker (22F) have worked together for about 3 years now and in that time have become very good friends, getting eachother birthday and Christmas presents and are friends on all platforms.

I wouldn't go as far to say I'm a touchy person, but I'm big into building team spirit and tend to give my female coworkers a hi five and my male coworkers a fist bump and everyone has a good time. However, within the last year or so I realised that my friend is very weird about any form of physical contact with me at all and it's like she almost recoils if we touch and so I just simply don't go near her because I figure it's not for her. Both of us are in relationships and as I said, we're friends so we text all the time but it's also only ever work related and there has never been any flirting.

I suppose however, my question comes from the fact rhat over the last few months I've noticed that she is a touchy person, and will touch me a lot like bouncing off my shoulders, or will touch other male coworkers and doesn't mind if they touch her which I find odd. We're both basically best friends at work, we're both in relationships and I respect her boundaries and figured that she may be against physical touch with men to respect her boyfriend, but I've noticed that this only applies to me and she seems so uncomfortable if we ever touch? Can someone help me explain why? And just in case, I'm not an unattractive person, and I would be the one to get the most female attention out of all the workforce, so I doubt it's repulsion, but I just don't get it, has anyone any ideas?

Trying to understand coworkers behavior?
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