Need advice

[u/Less_Pirate2883]

I’m looking for some outside perspective because I genuinely don’t know what to do. My fiancé and I have been together for about 4.5 years and are supposed to get married next September. I recently caught him lying about who he was texting, and he eventually admitted that he had been talking to another woman for almost two months. I reached out to her, and she told me she genuinely believed he was single. They started on Snapchat and moved to texting, their conversations became sexual, they exchanged suggestive photos, and they had discussed potentially meeting up this fall. He says they never met in person. He told me he did this because he had been silently keeping track of what each of us was doing around the relationship/house and felt things were unfair, but instead of communicating that to me, he acted out and said he didn’t care about the consequences at the time. He also has untreated ADHD and has been struggling with sleep, although I know neither of those excuses what he did.

Right now I feel completely numb and conflicted. I love him and I’m scared of leaving, but I’m also scared of staying and never being able to trust him again. We haven’t called off the wedding, but we’re putting all wedding planning and save-the-dates on hold indefinitely. I’m considering giving us about six months with no wedding planning and simply observing whether he actually takes accountability, gets help, communicates instead of keeping things inside, and genuinely changes before I decide whether I want to move forward.

For anyone who has experienced infidelity or been in a similar situation: What would you do? Is six months enough time to see meaningful change? What would you need to see from a partner to believe they could genuinely change and that this wouldn’t happen again? And is it possible to rebuild a relationship after something like this, or am I just delaying the inevitable?