Originally Posted by
Mer-Crazy
Because boys are weird? From the looks of it, and I swear I mean no disrespect to you or your boyfriend. I don't know him personally but this is just an observation of the behavior he has displayed in the text you provided. He seems to... fear... maybe? That by taking something like Taekwondo, he may feel emasculated maybe? He may want to retain this sense of being the physically strong one, a common attitude in males in relationships. They need to be the physically superior one, as they feel that being physically stronger makes them feel needed. A Self defense class like this may make him feel less needed or valued as a protector.
In that sense he would encourage you to undertake an activity that perhaps makes you more sexual? (I don't know but I suppose conventionally people see belly dancing as something at least minorly sexually provocative, intended or not, especially those who are ignorant as to the inner workings, like myself) If he supports your mermaiding then one could assume that this means he prefers his partner to do activities that are, at least some what provocative. This may also connect to the above statement, the more sexually you are portrayed, the more he will feel the need to protect you from others, specifically rival males.
Again I promise I mean no offence I'm just stating how it looks to me personally and I could be totally wrong. I don't know how guys think specifically, and I will readily admit that my views are probably incredibly sexist.