Even though he knew that it was "officially" okay for him to see others while in a relationship with you, he probably had fear of telling the two of you because of his own monogamistic conditioning / programming. Also, people in general, and men in particular, often have great difficulty talking about stuff that's difficult. Many of us never saw such talking "modelled" for us growing up in our families, or anywhere.... Where were we supposed to learn it? Well, those (like me) who fit the picture, learn via the sink-or-swim method. We're thrown into life. We f**k up a bunch, and finally we learn a thing or three.
Not everyone who likes to think of him or herself as "independent" is commitment or intimacy avoidant, but it may be worth honestly asking yourself whether that in any way pertains to you. I have no idea. Not even a hunch. But it may be worth asking yourself.
Those are my two cents for now.