Welcome to the Forum. On the Forum we try to note contradict what our clients' doctors have told them if there is room for an honest difference in opinion. In this situation however I agree with your doctor and disagree with the information that your BF has been told. Several points of clarification:
1. We all have yeast on most of our mucous membranes and from time to time due to a variety of causes, some persons may be at increased risk for getting yeast infections which are actually overgrowth of the yeast that is typically and normally present.
2. many factors predispose to yeast infection. these factors include taking systemic antibiotics (we often see yeast in women following antibiotic treatment), diabetes, and foreign bodies (such as your BF's plate)
3. Rarely persons performing oral sex on a partner with vaginal yeast infections can get thrush. This is through direct contact and as I said, it is quite rare.
4. In normal people yeast does not spread through the body from one place to another. your BF did not get his thrush from the spread of yeast from you to him and then through his bloodstream.
I think you two have ahd a bit of bad luck. I would not be otherwise concerned. Hope this helps. EWH