Need advice around uninviting someone behaving toxic after sending save the date

I hate this whole situation and struggle with doing anything like this as I feel I have an obligation to fulfill. However I really want to protect my peace and enjoy my day without the stress of wondering how this person will feel (especially as we have different values).

Backstory is I’ve sent a save the date to a work colleague who I thought I was friends with but recently (over 2 weeks now) they’ve been ignoring me and not really acknowledging my presence or hanging out like we used to. Their attitude towards me has become obvious they are angry and to the point where when we’re in the same room for a meeting or coming to see someone they give me the silent treatment. It’s really impacted me at work and it’s been ever since not being able to fulfil a last minute favour for them due to me having pre-existing plans.

I don’t feel comfortable approaching them due to them deflecting but I know I will have to.

I want to know what to do in this situation as I don’t want someone at my wedding who is showing me what the next year or so will be like if I upset them even slightly. But I also don’t want to be an A.H. by not sending them an invite after having sent them a save the date. Any (kind) advice would be much appreciated.