Two words for you
"Self control"
I think it is a normal part of life to sometimes have feelings for a different person to your spouse. It isn't because of lack of sex particularly and I think it will happen, probably more than once to everyone, although I guess a mismatch of libido can lead to it being more tempting to "entertain" thoughts and ideas of how a relationship with another person might be .
Remember you are not comparing like with like. You are comparing the reality of life with your wife with an imagined life with this other woman. In your imagination you can create everything that appeals to you with none of the downsides and difficulties that always come with a real relationship! Life with this other woman will not be how you imagine - it never can be!
Then I think it is a mistake to think that any one other person can meet all your needs. You are responsible for being in control of you own life and taking care of your physical spiritual and emotional needs. Your wife can't meet all your needs but neither will this other woman - thinking that is just fantasy.
So with all that in mind, maybe exercise some self control over your imagination. Literally dreaming about the other woman can't be helped not can feeling some emotional or physical "spark" or even arousal, but spending time actively daydreaming about it can be helped.
You made a lifetime commitment to your wife. Do you want to be the kind of person that discards this easily? Your wife deserves loyalty and respect. It may be that you do end up separating down the line but do you want to be a person that breaks a commitment for something that right now is an erotic fantasy.
Having said all of that, of course sex is an important part of a marriage and you need to address this at some point.
I'd not start off with talking to your wife about this though. I'd start by reminding yourself about why you married her, what qualities did/does she have that you appreciate. In what ways did she meet some of your needs ( bearing in mind no one person can meet all of them) and what needs does she meet now. What do you love about her. Spend time really just appreciating her without necessarily raising any issues with her.
This will mean that hopefully when you do start to talk to her about issues in the relationship, you will come from a place of genuine love and appreciation rather than " I want us to be closer so that I can have more sex" which would be a massive turn off for most women.
When you do start to talk about it, spend lots of time listening and trying to understand your wife's point of view. What is she feeling and why?
Don't necessarily rush to fix anything. Sometimes it is helpful to just sit with difficulties and differences for a while. Sometimes just hearing the other person and accepting the differences creates its own intimacy.
I don't know why you haven't had sex in so long and why your wife seems not to want it. As you discuss with her you will hopefully find this out. See what you can do to help her both practically and emotionally, not because you want more sex but because you love her and want good things for her.
It may be that down the line you and your wife decide to end your relationship but do this with the mutual consideration and respect it deserves.
Then and only then, once you have spent some time as a single person, aware of your own needs, strengths, weaknesses and processes, think about starting a relationship with someone else
tl:dr
grass.greener. Spend time really appreciating what you have. Your grass might be greener than you think and the greenness of the more distant grass might be illusory!