How should I confront my boyfriend about him hiding talking to his ex?

My boyfriend and I have been together for going on 3 yrs and we are expecting a child together. We have discussed his relationship with exes in the past. One particular woman contacted him to discuss her relationship issues. He said he has always been that type of "friend" to her. I asked him to stop speaking to her regarding those types of issues out of respect for me. It makes me uncomfortable to know he is an emotional crutch for another woman (who he has been intimate with). We plan on getting married and we live together, for this reason I don't feel we should hide anything from each other. I recently checked his phone and saw this woman has recently called him and requested his email (which he provided). This is not the first time she has reached out to him, but at this point I want to confront the issue. As I said, we spoke about this before and he agreed to not speak to this woman. It is frustruating to know he is speaking to her and sharing contact info and hiding it from me. I trust him and I am confident that he is loyal, but this is based on principle. I am very honest with him and he has never had a reason to doubt me, not then, not now and not ever. We share a home and soon a family. I will not be taken for a fool. I want to be tactful, cool calm and collected. Any words of wisdom?