cancer guy acting weird

i have been involved with a cancer for about 6 months, it is over the internet, and i care about him a great deal and he knows it. i send him an email once a day telling him i love him and care about him. he responds passively, but i will get to that a bit later. at one point he said he'd get angry over wanting something he couldn't have, and he couldn't think there was anything going on between us because he would get emotionally involved and that was "never a good thing". well, he's extremely moody, and i let him know i'm there for him, and he will passively say things to me in public forums. usually they are nice things, and everything was going well for a while, and he made this post about "leave me alone, you have messed things up and they can't be fixed", "i'm gone, are you happy now?" etc, (we had a trust issue where a jealous female that he is close to told him lies about me and he believed it) and then sent me an email telling me "you win, go have fun with all the others" and to leave him alone. it was very mean. the thing is, not too long ago, i told him not to be angry over wanting something he couldn't have, and that he would always have me, but on those forums (today) i had posted to another male giving him health advice. when he said "have fun with all the others" it felt like he took it as me placing my affections elsewhere. he has had outbursts like this in the past, and i'm wondering what is going on? are cancers really that sensitive? this is all really bizarre to me