I can definitely sympathize with you, my wife has a boyfriend and I've yet to have another partner; I understand the frustration it can bring, but as you will read (depending on a lot of variables) it is harder for men to find willing poly partners (that is, women who can share you emotionally).
I was jealous of my wife, and sometimes still am a little bit, because she has found multiple men willing to participate on an emotional level in a poly relationship. That being said jealousy is a secondary emotion, it is never caused by an event but rather caused by an emotional reaction to an event....you're wife has a partner, goes out, you feel scared she might leave (a common example) or you feel lonely and upset you're not going out (another example) so your reaction is to feel insecure and that leads to jealousy....So when you feel jealous, don't accept that your wife having a partner or going out is the cause of it, rather that it's your own mins creating the jealousy from insecurity or what have you...
More details are needed but what's keeping you from finding another partner? You cannot expect the clouds to open up and women willing to be in poly to fall from the sky...there's a scenario I faced called valley of the dolls and it basically boils down to opening a relationship up and then expecting a flood of available partners for you; it's not going to happen and like me you will need to accept that relationships progress along different timelines as do searches for partners...I also found meeting my wife's boyfriend to be particularly helpful and I developed a friendship with him that actually is independent of my wife...we're nerds, we talk nerd to each other...
What's stopping you from going out on your own? When my wife went out with her boyfriend the first few times I was anxious, jealous and lonely...because I isolated myself. Eventually I just filled my time with friends, the gym, anything I liked and that helped alleviate the loneliness (bear in mind, my wife will tell you, I'm an extrovert who can and will chat with anyone)
As for the question of fairness, have you discussed these feelings with your wife? Have you set guidelines? As a good rule, and if your wife isn't totally disregarding your feelings, her time and her relationship are in part subject to how comfortable you are, within reason. Guidelines for time spent together, how quickly her relationship progresses, etc need to be set but to be honest there are limits that you need to realize that you need to allow her relationship to grow naturally but not at the cost of your own well being.
Polyamory is wrong! It's Multiamory or Polyphilia. Mixing Greek and Latin roots? That's wrong.