I sympathise with you completely. Not dating can make you feel as if you are stuck in monogamy whilst she is out being poly. It can also be really hard to cope with the loss of time and attention from your wife, especially after five years, when you have no other romantic interest to focus on.
For example, my GF is definitely the most active one in our V. She's got a good key demographic: she's mostly straight, looking for men, she's a Domme, looking for submissive boys... they are all over the place where we live. She has no trouble finding anyone. She currently has myself and her husband as primaries, plus an online submissive, plus a new submissive in real life.
I have a smaller demographic: I want to find gay or bi women, who are poly, who are kinky, who don't mind me only being around for three months as a time, as I live in two different countries. I currently have my GF and that's it. I decided not to date any more, to focus on some self-growth and to stop leaving a trail of broken hearts behind every time I leave the country. Like you, I've started to struggle with feeling mono/poly and I've started looking again... but I'm coming up with nothing. This is frustrating... but I'm starting to wonder if that's fate's way of telling me I don't need to be looking right now... that there is something else I need to do.
Sometimes it is 'easier' or 'more fruitful' for our partners. It's generally easier to find eager straight men than it is to find women. That can be hard. The best thing we can do, though, is to look at what we have and look at the opportunities within that. I've stopped thinking that to 'be' poly, I have to be dating other people. I AM poly, because I am sharing my girlfriend with other people and I support it and am still here. So now, instead of continuing my quest for another lover, I'm looking at it more like "I'm in a poly relationship - that means if I do come across someone I connect with, I am free to explore it". That gives me hope and some peace. I know that if I was mono, I would be forced to deny any future potential.
Ways to manage it:
It sounds ridiculous... after five years, you've probably done a lot of this. But... filling your time? Focussing on yourself? Every time I am not dating and my girlfriend is, I learn to become stronger, more independent, more self-sufficient. It's painful, yet feels good in the longrun. And, the cherry on my sundae is that I do have a girlfriend, who I love more than anything. You have your wife too
How about other ways of getting interaction, like online? I play in Utherverse, which is like Second Life, but kinkier, and these connections really take the edge off for me when I feel lonely.
The other thing is looking at your interactions with potential dates. Ask yourself honestly - after five years, are you chomping at the bit? Could you be coming across as too eager, too needy, too pushy, with new people, because you're so excited? Warning signs that this might be an issue are things like... always texting them first, continuing to contact them even if they haven't replied, being too strong with the wordage too soon ("you're amazing" "I could fall for you" after a couple of weeks, etc).
I do have one final thought. How is your wife in terms of 'overshare'? I've asked my girlfriend to keep details of her other pursuits away from my ears for a while, because I'm currently going through a tough time. She carries on blurting stuff out anyway. Over the past few days, she's told me about how much she laughed with her new guy on their date, the beach walk they had in the rain, whether she should take condoms to their date, how amazingly stunning his house is, how they had a 'nice private goodnight' in his bedroom, asked me for help picking out her date outfit, how easy and fun it is to be with him, how her biceps hurt today (i.e. after spanking him all night), how much of a rush she was getting from Top High, how she had rough sex with her husband in the morning, what she told him during sex, what he did to her, BLAH BLAH BLAH. Too. Much. Information.
Now... normally, I like to hear about her and her husband (not so much about new dates). I am aware, in myself, that I cannot handle it at the moment. We are in an LDR with 3 months together, 3 months apart. I have realised that when I am feeling neglected / loss of something / unfulfilled, envy starts to spike. I'm not having sex with my GF at the moment, because we're apart. Envy is spiked. I'm not having romantic time with her, because we are apart. Envy is spiked. Every time she tells me something, envy is spiked. This is starting to go from envy about other people being with her to envy about ME not having someone else. Why do I want someone else? Well, at the moment, it's because my needs are not being met. I feel lonely in my primary relationship; which is exasperated by the fact that her time is focused on others. It has started to make me envious that she is having these experiences, because I'm now wanting them, as a distraction from the void that I feel in our relationship.
What I mean is - I am poly in the sense that I am open. I do not NEED other relationships. When I am with my girlfriend, when things are good, sex is good, love is good, my desire for other relationships is way, way, way less urgent. I'm still open, but do not crave it. When things aren't good, sex is non-existent, she doesn't make time for me, or doesn't seem excited by me, I crave other relationships much more and feel MORE bad about struggling to find them.
So... my question to you is - is anything else going on here? Is it five years of no other dating that's getting you down, or is something triggering your envy? Do you feel lonely in your relationship? Do you feel neglected at all? Is your wife considerate? Are there any little niggles here that are getting you down and making your almost mono/poly feel worse? Does your wife make time for you, as well as her other relationships? Or is it purely, one hundred percent, that you want to experience other relationships?