Have you ever been a relationship third-party?

Asking for a friend, jk. Please hear me out. When I started my first job I've been really close with my senior who was turning over her job to me and same with our chief engr. (they are quite a famous couple on our office even tho he always deny it). As the youngest employee they often bring me along and treated me as a child, also they have a bit of an age gap w/ me so I often ship them together. When my senior resigned, I remain as friends with our chief and we often hang out together. But not so long ago I felt that I'm falling for him, at the same time he confessed to me about his own feelings (he said that he like me for some time now). I didn't meant for everything to happen, I thought it will be like a simple unrequited crush. I want to distance myself but I think the truth is I like him a lot? What will you guys do in this situation? (I thought this only happens in stories)