The joy of being in a relationship with a Cancer is, not only do you receive heavy Cancerean influences - you also get heavy influences of their Moon sign. A Cancer with an Aquarius Moon (like myself) is going to be much less moody and hyper sensitive than a Cancer with a Pisces Moon. The emotions will always be there - regardless of the Moon sign. However, the Moon sign will dictate how they process and express their emotions.
Then, you also have to factor in the House that the Cancer Sun is in. Mine is in the 11th House, giving me an Aquarian aspect to my Cancer Sun. I don't know what this Cancer's chart looks like since I don't have the date, location and time of birth, but if you really want to understand your Cancer better, I would recommend acquiring those pieces of information if you haven't already.
Also, it may not be a bad idea to take a look at your chart next to his chart. Synastry is very powerful and really helps shed light on the promising aspects of your relationship and the potential difficulties.
Peace and Love, CALLTV