There looks like a growth or something above his mouth infront of his right eye.
If you think he is suffering and if you know what you are doing which i guess you must if you have bred bettas then you should put him out of his missery.
I have heard the best method is to put them in a small bag with just enough water to cover their body then put them in the freezer. Fish do not feel any pain when there is a slow change in temperature, especially if they are ill, so he will just fall asleep and his body will switch off. After an hour or 2 take the bag out and dispose of it how you please (I bury all my fish, sad but respectful.)
Ben