Yes I have been in your position lostmale and it’s really tough, you have all my sympathies.
So from someone who really does know, it is impossible to just ignore and why should you? You are not a lodger, you are a parental figure and your wife needs to wise up. You have been living there for 4.5 years, that is time enough to be able to also have a say in minimum rules and standards in your house.
Your wife is undermining you by not allowing you to be parental - because as you say - you ARE being parental anyway in ways that she ‘approves’ like providing rent, housework, doing nice things with your step son. Your step son and wife can’t have it only one way.
I am also talking as someone who has a son, who has/(had) a step Dad and I did not undermine my DP. Yes, sometimes he was too heavy handed, we talked about it. There has to be some middle ground, some negotiation - you can’t be the ‘boss’ and yet you can’t be ignored totally either parentally. It’s tricky but it can be done.
I would have a really, really frank talk with your wife and say that you are in a parental role and need to be heard. Say that you are prepared to accept some things that you don’t necessarily agree with (please mean this - you must let a lot of things go) - but pick say three things that you’d like to see SOME change (you must be prepared to not get everything!). But stick to this.
Go to couples counselling if this does not work.
Then sit down, together, with your step son and put up the new rules. He’ll kick off, she’ll probably cave in sometimes. Just keep calm and don’t shout or lose your rag. That’s important, you are a step Dad and any shouting or even mildly aggressive stances are going to be way more intimidating for your step son than if you were his father - as you haven’t got a well of love to balance out feeling cross with him - so being really gentle too.
Your step son also is probably crying out to be treated as more of an adult and anything you can do to bolster this will really help him. Even if you join in a computer game with him - just for a while - or take him to something he might love like go karting.
In fact none of this will work unless you also find a ‘way in’ to your step sons heart, even in a small way, bribe him a little by buying some small things for him - some chocolate or drinks. These small things will show both him and your wife that rules are out of a position of care rather than authority.
Good luck. 