I hope this won't get out into some YT video or TikTok, so please don't share this on other social media.

Also, I don't speak English fluently, so I apologise beforehand.

TL;DR:
Due to partner's behaviour before the breakup, there is an almost guarantee chance that she has been at least emotionally cheating with her coworker right before breaking up with me. We want to live together and co-parent as long as possible. But knowing there is more to the break-up, I don't know how to proceed.

Break-up:
The break-up happened a few days ago. I am taking the blame for our relationship going downhill. In the last few months, we have lived more like roommates than a couple. We had a good relationship until the burdens of my mental health started to spill on to her, who also has to deal with her own mental issues. We were good for each other when we met, we are still good parents to our only child, but we are now on a different path. I am starting to make peace with it. I still love her, but my inability to be a reliable partner has become too much for her to bear, and doesn't seem like she has any more patience/tolerance to wait for me to get my shit together with my psychologist.

I don't mind not being romantically involved anymore. We decided to co-parent and live together until our child is old enough for us to look for other options. I just want my child to grow up with both parents present. Apparently there is a sliver of change that we might end up together again. However, this new turn of events is leaving me scared, confused, disappointed, and angry.

Before breakup:
She just started working at a new place a few weeks ago and would mention her male coworker quite a lot. She is usually flirty, but I could tell it was a bit more with this guy. She seemed so desperate to be friends with him. I know that I have been feeling inferior and had lower self-esteem than usual due to my shortcomings, so I just chalked my suspicions up to feeling of jealousy due to my lower mental health state and stress. So I pushed my feelings aside and gave her some advice on how to approach her coworker.

I've started noticing that she has been taking a lot of selfies and also protective of her mobile devices. She started to doll herself up, even though she wasn't going anywhere. Sometimes spending 15-20mins locked in the bathroom having a "self-care time". She suffers from very low self-esteem and chronic depression, so I was just happy that she has come out of her shell and feel confident.

After breakup:
Although it happened amicably, and we discussed almost everything about our relationship, things still don't completely add up to me. Looking back at her behaviour in the last 2 weeks, it started to dawn on me that there may be more to it than she is letting on. She has been adamant that she is not looking for any relationships while we are co-parenting under the same house. I have never had a reason to distrust her, but this time my senses are screaming at me. It's the exact behaviour when we started dating.

At this point, I am almost convinced I have enough reason to snoop her phone/tablet to check their messages, and not feel morally wrong. And I am 99% sure I will find shit that will haunt me for the foreseeable future.

We are telling her mother together about the change in our relationship this weekend. I am fantasising about making her show her chats in front of both of me and her mother.

I don't know what to do. My daughter is my priority. My partner has been cheated on in the past, I never thought she would be the one to do this.

I want to keep this issue silent, but at the same time I want to confront her as this is a violation of trust, which we need for co-parenting. At the same time, I do not want to upset the current arrangement, and feel like I should just keep it to myself and see where this will lead.

I need to sleep. I am low-key hoping I won't wake up. Or I do and this is all a dream. But I have to for myself and my child.

Sorry if this post is incoherent and over-dramatic. I am crying. I don't have anyone to talk to about this until I see my psychologist in a few weeks.