I'm also a centrist who tends to lean towards Biden (I also really like Senator Klobuchar), but I do take issue with you saying you want Donald out of office as much as the rest of us, but then go on to say that you have a feeling you're "going to be voting third party again."
A vote for a third party candidate is the exact same thing as voting for a 2nd Donald term.
This election is about one thing - removing Donald from office. If my choice is Bernie (Lord, help us) or Donald then I will vote for Bernie in a heartbeat and then sit back and watch as every one of his fanciful promises are swatted down by Congress.
If my choice is Warren (not nearly as big of a demagogue as Bernie) or Donald then I will vote for Warren. A Warren Presidency would be interesting because she actually has specific policy proposals, like them or not, that Congress could take up if they chose.
If my choice is Dwayne "The Rock" Johnson or Donald then I'll don a Baywatch tanktop and cast my vote for the dreamboat.
I will vote for whoever has a D next to their name in the general election even if it means I have to swallow hard before casting my ballot. This election is about so much more than my feelings. It's about saving our country from a narcissistic sociopath who is currently in control of our nuclear arsenal.
So if you vote third party then you are voting to keep Donald in office. It's as simple as that.