honesty has always been very important for us.
on one hand i can understand him not telling you ahead of time if he was only being half assed about searching. although it does not sound like it was half assed.
on the other hand, when asked, it should have been no big deal for him to tell you what he was thinking / doing.
the rub is that it seems there is a history of this behavior, and not telling you about ongoing relationships is a bit over the top.
i think maybe a sit down is in order, for a good talk about open communication and foreknowledge of activities planned or hoped for. let him know how it makes you feel, and that you are needing a change in that behavior.
i can only hope it gets better for you.