We agreed to open our relationship, but that was years ago

My wife and I have decided to open our marriage a couple of years ago. We never acted on in because in our area it's hard to find people who are open to the relationship. A couple of months ago I started talking to another woman. Well in that couple of months I've started developing feelings for her. Would I be over stepping my bounds if I were to tell her so, or should I talk to my wife about it?

You should talk to your wife about this first. Don't rely on an agreement you made years ago to have gone completely unchanged in the meantime. I'm sure I agreed to things in 2015 that I would not like to be held to today! Open relationships require lots of communication; it's not a one-and-done sort of thing.

So bring it up again - "hey, remember when we talked about opening our marriage? I know it never really worked out for us to put that agreement into practice, but I'm in a situation now where I might actually want to try dating someone else. Let's talk about it again, now in the context of where we are today, what might have changed, and our specific situation right now."