jealousy?

Dear all, I would be glad for any advice and insight. I am married for fifteen years, with two kids. Two years ago I realized my husband was emailing his female coworker with messages indicating friendship and some sort of emotional bond. I met her once. It was, I believe, budding friendship rather than romance, but it was too much for me. It was just too emotional, at times lyrical - sharing your interest in particular passage of books, emotions about some places, exchanging music interests etc. Once or twice I caught him lying (he borrowed a book from her but told me it was from someone else). I talked to him; he said it was innocent, he was unaware that it might be a problem; he never thought of her as a woman really; was deeply disturbed and decided to make the relationship entirely professional. Now we are two years later. They work closely together. She is a kind and helping soul and helps him with everything both professionally and not. Like making sure he eats, getting stuff he needs, getting things for our kids, taking care of our cat when we are leaving. We travel somewhere and he emails her after 20 hours flight to let her know that we are ok because she is worried. I can not bear it anymore. I feel that she is intruding into our marriage, into my space. I talked to my husband and he said that yes, it is some sort of friendship, she is so helpful and he can not just not respond to it. He said that if he was in my shoes, he would make sure to get to know my friend. The thing is I was so traumatized two years ago I wouldn't dream of meeting her. I trust my husband - I do not suspect him of infidelity. He does care about me and is concerned about the problem. But I can not bear the thought that unknown woman has so much access to his emotional life, is on track with everything what is going on in our family, is in his thoughts (writing an email after 20 hours flight?!). I believe that we may have different understanding of personal / marital space. I really do not know what I should do. Is the problem in me? Would it be an issue for other women? I would be grateful for any comments...

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