Why would two coworkers try to hide their relationship from me but not from others?

For instance when they would be chatting on teams and saw me entering the office one of them would change their status from „in a call“ to „available“. At first I thought this was just a coincidence but this happened 3 times now. I once overheard him flirting with her and both of them tend to sneak off alone pretty often when they are both in the office. Both of them are married with kids and don’t plan on leaving their partners anytime soon. I know this is not my business but I’m still curious why they would try to hide it from me when everyone already knows since they are always so obvious about it?

Why would two coworkers try to hide their relationship from me but not from others?
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