@lodger I mean this kindly, but I'm not sure you are cut out for having a lodger - at least not at the moment, when you have just moved home to a brand new area and your DH only passed last year?
You have referred to Boundaries being pushed, several times, but the thing is, that from your posts, it appears that most of the boundaries when this man moved in were in your head rather than being communicated to him. Neither of you are wrong, just not singing from the same hymn sheet.
I'm glad that you have spoken to him, but you need to think carefully about what your boundaries are and what you can live with. You need to think it all through and not drip-feed to your lodger, more and more things that you don't like, as time goes on, that irritate you. That's par for the course when you have someone else living in the house - they are not children. It's not a fully contained area that you have to rent out. Any lodger is going to need to use the kitchen. Some more minor irritations will need to be lived with. If you can't do that ( and yes it is your house, and it's not at all unreasonable for you to feel that way), then maybe taking a lodger isn't for you at all? Not fair to you and not fair to any potential lodger?
You need to be very clear in your own mind, as to what the actual boundaries are, and agree them with any potential lodger. Thus far and no further type boundaries. Little irritations WILL happen with any lodger
The GF shouldn't have come into the living room without at least knocking, but you are possibly reading too much into her tone of voice? Curious to know what you said to her when she said that? I would have said something like 'Yes, it is a big house, which is why I thought I would take in a lodger as I have all that space upstairs'. Only need to share the Kitchen and it is a big room!
Hope you can sort things out with the current lodger, but as I say, decide what the ground rules that really matter to you are, write them down into a contract and go over them with any future lodger.
You could also tell your current lodger that you haven't taken in lodgers before and you are sorry that you didn't communicate properly at the beginning about the boundaries and let him see what the contract will be going forward?