"My SO knows that if I ignore how I feel and force myself to be mono I'll be basically living a lie. I'll be having to supress part of myself and avoid forming close ties with other women just in case. Either that or basically I'll end up cheating eventually. Something I have never done before but we had to consider it as an option."
You and your SO considered cheating as an option? Doesn't that mean she was prospectively giving you permission to cheat? By definition that would be polyamory rather than cheating. Do you mean that she thought it might be okay for you to have another relationship as long as she never found out about it? a don't-ask-don't-tell type of agreement?
My situation is a V in which I am one of the "arms of the V." So I only have one SO, even though that SO has two romantic partners. I'm sure I'm capable of falling in love with an additional person, but I don't feel any great need to go looking. So you could say "I'm poly" even though my situation "is mono" from my end of the V.
Ry (FullofLove1052) is the only case I can think of offhand where there's a "regular monogamous couple" where one of the partners could be poly (and has been poly), but is now living monogamously for the sake of her spouse (and as it turns out, also for her own sake). But I suspect there are quite a few cases of a monogamous couple where one partner would live polyamorously "if they could," and yet that "would-be poly" partner is happy enough in the monogamous relationship. There seems to me to be different degrees of how intense someone's urge to be poly is. For some people it's not as big of a deal as it is for others.
It sounds like being/living poly is a big deal for you. But you have quite a dilemma on your hands if living polyamorously causes you to feel like you're cheating and makes you miserable in that sense. It sounds like you're doomed to misery regardless of whether you live polyamorously.
Unless this feeling of "I'm cheating" stems from your SO's dislike for the polyamorous situation? If so, then perhaps you need to find out whether she can get past that dislike. If it stems from a fear that you're going to leave her for someone else, then maybe there are things you can do to reassure her. If she feels jealous about sharing your time and attention, maybe you can allocate special date nights with her or something that might help "make up for it" in her mind. If she feels that polyamory is immoral, maybe she could read up on poly or even join a poly forum like this one and get some "unconditioning for her conditioning."
What the others are saying about the possibility that you and your SO might not be meant to stay together, and about the need for more study and preparation before you "test out an actual poly situation," also has merit and should be taken into account. If the two of you could find a poly-friendly counselor to talk to, that would certainly be awesome. It seems to me that you both need some more time to talk, think, study, and communicate, before making any heavy decisions.
There's a particularly good book about responsible non-monogamy called "Opening Up," by Tristan Taormino. Perhaps you and your SO could read that book together, and talk with each other about whatever thoughts or feelings each reading engenders. Just one possible activity that could help.
I hope you're able to get some things sorted out. Don't hesitate to do some more posts if there's some more questions we can answer, etc.