Re: guitarest issue...
The best way to look at any band problem is like this.
"Am i being as professional as i could be?" Even if you have to kick someone out who is your best friend, so that you could be happy playing music. You should. If he is also asking him self the question "Am i being as professional as i could be?" -As he should be- Then he would understand that you guys need someone else, or you need him to improve.
Hopefuly it works out for you.