Hello Solost: I noticed this is your first post here on PC. So... welcome to Psych Central.

I'm sorry I don't think there is much I can offer with regard to this difficult situation. I'm quite sure your partner is feeling depressed, anxious, guilty, perhaps ashamed, scared, confused, & probably a few more emotions I haven't thought to add to the list. I would guess it is, perhaps, too painful for him to do what both he & you need to do... talk about it. And even if he could find it within himself to talk about what he did, he likely would not know what to say or how to say it.

So I'm afraid that leaves you to figure out what to do in response to this situation. Ultimately, you can only change yourself. And you only have control over what you do. So, at least from my perspective, I would think what may be important here is to not spend too much time trying to understand how something like this could have happened to begin with; but rather focus your energies on deciding what you want to do for yourself given the circumstances with which you are confronted. All of this may be something you'll want to talk through, at-length & in-depth, with a counselor or mental health therapist.

Here are links to 10 articles, from Psych Central's archives, that talk about how to respond to infidelity:

Can Your Relationship Survive After Cheating?

5 Unexpected Emotions You Will Feel After Discovering An Affair

Surviving Infidelity Requires the Partner Who Strayed to Accept 100% Responsibility for the Affair

Surviving Infidelity Requires the Partner Who Strayed to Feel Genuine Remorse

Surviving Infidelity: Why It's Necessary to Prove That the Affair Has Ended

https://blogs.psychcentral.com/infid...ated-now-what/

https://blogs.psychcentral.com/infid...dium=popular17

https://blogs.psychcentral.com/infid...dium=popular17

https://blogs.psychcentral.com/infid...dium=popular17

https://pro.psychcentral.com/recover...spouse-cheats/

I hope you find PC to be of benefit.