I think the important thing to remember here is it is okay, and even good at times, to BASE a character off yourself as long as the character ISN’T you. Just because you used yourself as inspiration doesn’t mean that the character must act like you all the time.
I am seeing two separate questions in this question. One: people don’t know themselves well enough to make a character based off themselves, so why bother? To that I say, so what? The point isn’t to make themselves a character, the point is to make a true-to-life character, and just because you are incorrect about yourself doesn’t mean that the character is bad.
The second question is: how do I make the character interesting again? The answer is the same for characters you didn’t base off yourself. Maybe you should change them. Take a break and come back to the story when you aren’t so bored of it. Remember what attracted you to this character in the first place, why he fit with this story.
I hope that helps.
The cake is a lie. acaylor.com