OMG~you were born 2 days before me~cool

Most of wat is happening for you here is your own paranoia if you don't stop being so suspicious what you fear will become reality and he will blame you for not trusting him enough, for driving him into anothers arms.
He is only being so flirty because he enjoys the attention he recieves but theres not alot more to it. He is very serious and moody by nature which is a hard thing for a social, chatty, bubbly butterly such as yrself to cope with. Perhaps for this reason you are not very well matched but you can make it work if thats what you truly desire. You need to let him have his space and try not to get inside his head all the time. If you have a dissagreement and he walks out, let him go for a walk/drive and cool down for a while thats his coping mechanism he's not going off to see another woman he just needs to be alone for a while.
Don't try to re-start the discussion when he gets back either just try to bite your lip and be happy if you do this he will communicate to you more as he wont feel like hes being interrogated.
Peace be with you