Colleagues send text messages to their husbands, but they don't reply.

I can see that this female colleague has a good relationship with your boyfriend. Just to be on the safe side, you and your boyfriend invite that female colleague out for dinner or something. Since she is your boyfriend's good colleague and friend, and you said that you also want to know her, I don't think your boyfriend will object (if he objects, it proves that he is guilty). In the process of eating, let her know how deep you are with your boyfriend in an indirect way, suggesting that she should not be too ambiguous about your boyfriend.