You were together for 18 years? Forgive me if I have the length of time wrong. I'm seperated for 15 months and almost 8 years with the ex.
The length of time for grieving is different for everyone and closure of a LTR is measured with the length of time that you had in the r/s. It's not a definitive clear time line OK I will be better by such and such a date.
Infidelity is a difficult thing to process. For me it went against my core values and the value I hold with a covenant that is sacred between two people. I took my end very seriously and I have second thoughts on certain men she was friends with, was there an emotional affair? I felt violated and a fundamental foundation of trust between two people destroyed. It's tough when the other spouse doesn't validate that. Life goes on for them and its as if nothing happened, disassociate. I accept, but there are times when I get triggered no doubt. I see her when we exchange kids, I have PTSD triggered throughout my body and see her with a false facade, she looks happy and invalidates what we had. We both have a right to our anger, but to work through healthy anger. It's going to take some time to put all of this behind. A non disordered r/s can take years for either to get to a position where there's no malcontent between each other. I see it as were still in the early phases of separation and divorce. Having your ex so close to you, mine as well

doesn't help. It feels like scabs re-open and it triggers feelings and memories and I see the replacement ever now and then. The nonchalant attitude both have hurts.
NC is a tool to heal and to get out of the FOG. Forgiveness is something you will have to look into to your heart to find. I think your anger is from grieving and you can't deal with 18 years in my opinion in a year. You feel the difference, so do I because I feel like I have taken control back of my life and confidence that things are going to get better. There's no reason to stay in her FOG, it distorts and takes away your self-esteem and triggers feelings.
Do you think that you may not be completely over grieving?
Have you thought of moving? I'm moving out of this neighborhood I live in. I shared a lot if memories and its time to move on. I think you need to reframe this as going easy on yourself and looking at this in the Longview. It's a matter of time and it will come, forgiveness and letting go of that residual anger. She broke a trust a contract that's hard.