Is AUTHOR wrong in the post ? POST : Hey arbiters of assholiness!

I've lived with my roommate for just about two years now. His previous roommate moved out and I signed a new lease with him. That new lease expired about 10 months ago and since it expired, we've just been living month-to-month with no lease. This was my roommate's idea because the landlord didn't really care and without a new lease, the landlord wasn't going to increase the rent. I didn't love the idea at the time for reasons I'll get into in a bit, but I agreed to it anyway.

Recently, my girlfriend and I decided to move in together. While we are looking at other apartments in the area, the apartment I'm currently in fits the bill of what we're looking for perfectly and there hasn't been on a lease for a while, so I reached out to my landlord and offered to sign a new lease with just myself and my girlfriend (several months from now, wanted to give plenty of notice). Before doing any of this, I sat down with my roommate, explained the situation, and encouraged him to also reach out to the landlord with the same offer if he's also interested in snagging the apartment himself and we'll just leave the decision in the hands of our landlord.

Initially he seemed cool with this but last night, he confronted me and tried to guilt/pressure me into rescinding my interest in the place and just move out, saying that he's been in the apartment for longer (only by a couple months), I'm the one who moved in, etc, so he should get to keep it. There is one other element of this worth mentioning:

In the last month of our previous lease (so around 10 months ago), his girlfriend moved out of her apartment and moved in "with her parents". In reality, she started spending 7 nights/week at our place and has lived here full time since then without paying rent. He did not ask me if I was okay with this, said that it would be temporary, and his timing was impeccable as the terms of our lease (which was about to expire) VERY clearly stated it was for two tenants and anyone who spends more than 10 nights per month in the apartment is considered a tenant. However, with the lease expired, I didn't want to make any waves since the landlord knows him better and I couldn't afford to potentially get kicked out and replaced by his girlfriend for bringing it up. 

The way I see it, I'm giving both roommates/couples equal footing to vie for the apartment. Yes, I'm the one disrupting the status quo here, but the status quo was an unfair situation that was taking advantage of me and my financial inability to escape it. The way he sees it, its not my apartment to vie for and he should get to keep it without involving the landlord by virtue of being here first.

Am I the dick here, is he, or are we both two assholes who deserve each other?