He even professes to be a Christian now. However, he has a habit of muttering very disrespectful things under his breath. I have addressed this with him many times over the past year or so,
It is possible you don't have to listen to him. It depends on what is really going on.
and now i am finding it very hard to forgive him and very hard to even be around him.
Well . . . Jesus makes it easy to forgive. We need to get stronger in Jesus' love so we can be generously forgiving. This is needed first, maybe

I mean, maybe > when others still can get the better of us, this can mean I still am not strong like I need to be . . . so then people can't get to me, plus I can forgive them and pray for them and care about them with compassion. So, maybe God will "allow" "things" to keep happening . . . until I get with Him the way I need to. In my case, anyway, it has been like this for me. Once I get it right . . . all of a sudden, even, certain things can disappear, even.
So, if you need real change about forgiving, then it is maybe even likely that you could go somewhere else and the same problem will be ready and waiting. Or, Jamie could be removed, then some other item person would come along.
It might have been like this with our Apostle Paul > 2 Corinthians 12:7-15 < have you read and fed on Paul's "thorn in the flesh" experience?
My take is his "thorn" was a demon who had various powers to work Paul over like a boxer using jabs and swings and combinations to test and wear out his opponent and then get to him through his weak spots. And Paul was getting pretty displeased at how things could get to Paul who was supposed to be so strong and mature and our so great of a church leader and example.
And Jesus would not quick-fix it.
Paul had to discover how to live in God's grace which would give him almighty rest plus our Creator's creativity for how to take advantage of any trouble and use it for God's all-loving good > > > **n-o-t** only to make things nicer to Paul.
So, may be you have something in common with our great Apostle Paul!
It is at the point where it is affecting the business adversely and i am strongly considering leaving the family business.
How do you mean this? Is Jamie saying things against other people and this is causing you to lose business? Or, do you mean he is distracting to you? Or both??
Anyway, now you have us praying for you. Let us know, please, how you are doing. What helps you could help me and others, too, you know.