I am sorry that you go through such a rough time. Your 'poly-journey' isn't something I enjoyed reading. It feels wrong on many different levels.
First of all: don't try to be someone you simply are not. If you are mono, you simply are. Fullstop. Don't try to 'be a good "poly" guy' if you don't feel like that. If you don't need another relationship, don't force one onto yourself.
And the biggest issue I have with your situation: What kind of attitude is your wife giving you there?! That's gross and unbelievable kind of. She doesn't have time to work on her relationship and heal the wounds she inflicted on you? She doesn't respect your boundaries and went on to do her thing, cheated on you and lied to you about everything and when she finally came straight about it, she told you she didn't thought that you could be hurt because you stated that you would be OK with that much? That's utterly bullshit.
I take that she is still seeing this other guy? If this is the case, she is satisfied and is neglecting you in regard to intimacy now and tells you to go look elsewhere? Does this woman care about you at all? This sounds like someone who is abusing you, only taking and staying in the situation because it is comfortable for her (you paying the bills and such). Please correct me if I am wrong, but that is the kind of input that I got out of it.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.