Was this wrong?Or am I overeacting?To what he did?

My boyfriend went back to school for nursing.His first class he had a fremale married lab partner.When class ended she wanted to stay in touch she ask for his phone numberHe said no his girlfriend wouldnt like that.Week later said she really wanted to stay in touch.What about his email?He gave to her.He emailed her every few months about his clininclas.One tiem he went and sold her a book never told me.In one of the emais he told her maybe they coudl grab abite to eat and he could tell her everthing she wanted to know about his nursing clinincals.I was hurt by that.Also one weekend he went on a saturday and she showed up with pb and jelly and snacks .He took a break she offerd him he accepted.Five min break.Also never told me.See heis very quiet ,shy introvert.She was friendly he liked that.But he never told me I feel betrayed what do you think?We live together own our home.Were together for seven years when this happened .She lost his email so he never wrote her again .Then sent a email to teh college they foreard it to home email .I saw himreading it thats how I found out.