OMG I am really glad to hear that! Thanks so much BlueHaven! I thought because I bought him already with fin rot, that he will be stressed and miserable forever, but if this is the case then thats awesome!!
Though it is a perfectly normal behavior for bettas it is not necessarily a sign that they are happy. That is a common myth ;) It is more of a territorial action and a sign that he will be ready to breed should a female come swimming by. However, it is always a wonderfully rewarding thing to see :)