How do I limit the trauma my (33M) soon-to-be-ex wife's (30F) daughter (8F) experiences?

My wife and I got married 2 months after I found out that she was pregnant, we hadn't been seeing each other for very long but I wanted to do "the right thing" and make sure that my child would grow up in a proper family unit. Over the years, I did actually end up falling for my wife so it seemed like everything would be perfect. I had a beautiful little girl, a wife who I thought loved me and a very well paying job.

Fast forward to a few months ago and I discovered evidence that my wife was sleeping with at least 2 other men before we got married. I tried to forgive and forget since we weren't exactly a couple at the time but then the suspicions got to me. My daughter and I look nothing alike, family and friends have always joked that maybe she was switched in the hospital but I slowly came to the realization that my daughter may not be mine.

Shortly after that I ordered a paternity test and as you can probably tell by now, she's not mine. A second paternity test later, I completely fell apart. I didn't let anyone else except my parents know what was happening but it was like the perfect life that I had tried so hard to build was falling apart around me. I became depressed and even started drinking. During this time, I didn't know what my next steps would be so didn't tell my wife. With my parents help, I picked myself back up.

She must have known that there was a chance that I wasn't the father. I think she chose me specifically out of all her lovers because she knew that I would be able to provide her and her child the best life. Reconciliation is out of of the question but I can't divorce her. She's never had a job and only has a high-school education so that would mean I would be absolutely decimated with alimony. To make matters worse, my lawyer says that it's unlikely I'll be able to disestablish paternity after 8 years so she'd be getting child support payments too. In short, I'd have to give up half my paycheck when the last thing I want to do is support my wife for another 8 years.

It's clear now that remaining within this country's jurisdiction is no longer an option so I've been looking for a job in another country and received news this morning that I've been accepted for a great position. All that I have to do now is liquidate my assets which shouldn't be hard since everything is in my name except our home which we rent.

I know that I shouldn't feel guilty about any of this since I have no connections here and none of this is my fault but I don't want my daughter's life to be ruined by this. It's very likely that after I leave, she and her mother will be living off of government assistance but I still want her to have a future so I'm planning on opening a college tuition account for her.

I haven't decided yet whether I'm going to tell her that I'm leaving or whether I should just let my wife come up with an explanation and that's where I need help. I want to do this with as little trauma to her as possible so would it hurt her less for me to tell her that I'm not her dad or just disappear? Has anyone else been in a similar position to this?

TL;DR: I found out that my daughter isn't mine. If I stay in this country, I'll have to support my wife which is exactly why she tricked and married me in the first place. I'm planning on leaving after the pandemic but is it better that I just disappear or let her know why I'm leaving?

UPDATE:

It's been some time since I posted about my situation, I wasn't going to make an update because I didn't even know what to say but I've been getting a lot of requests for one and I have a lot of spare time so here it is, I think I'll just start from where the last one left off.

The day before I left, I wanted to give my daughter one last great memory of me. We took her to the beach when she was younger and she always asked if we can go back one day and I knew that it would be perfect. I don't know why I expected it to be easy but it was far from it and I'm not ashamed to say that I almost cried a few times but I kept myself composed because I wanted to give her the best day ever and I didn't want my STBXW to be suspicious.

We got ice cream, built a sandcastle, collected shells, destroyed the sandcastle and had dinner at a restaurant overlooking the sea. I don't think she stopped smiling even once the entire time. Despite trying my best to hide it, I also think my STBXW noticed that I was sad and I think she tried to be extra affectionate. For a moment it felt like before when we were a proper family but I had to force myself to get past it and face the reality that it was all just a lie no matter how much I wanted to believe that they were my family.

I called my STBXW from the airport the next day half an hour before my flight was due to take off and I told her what I had discovered and this is where I actually did cry. I told her "What you did was disgusting and the pain you're about to put our (your) daughter through is no-one elses fault but yours". She stayed silent for most of the call which confirmed my suspicion that she at least suspected it but when I told her that I was about to leave the country and I wouldn't be coming back, she started to panic and told me that we can talk about this and that this doesn't have to be the end. I said that I would call her soon once I've settled.

The past month and a half have been chaotic. At first she just refused to accept the possibility that we were done, that this was just me being rash and how could I even think about doing this to our daughter who loves me so much. During this time she called me regularly trying to manipulate me by saying that our daughter was asking for me and passing the phone to her, I didn't really know how to explain this to her but I've decided to leave that up to my STBXW. When she asks, I just tell her that I'm going to working away from home for a while.

When my STBW finally realized that this was happening, her initial reaction was to say that they would be ok without me and that it would be best if daughter stopped talking to me so that she could have the chance to move on and forget about me. That lasted about a week and I hated not knowing what was happening. Eventually STBXW called me back saying that this wouldn't work because daughter has been asking to talk to me non-stop.

Now STBXW is switching tactics again and saying that if biology is so important to me, to please come back and we can start trying for kids. This is the only time I faltered a little because before she insisted that we wait until our daughter is a little older before we have anymore but I've always wanted to have a son that I could share my hobbies with. I know the type of selfish person she is now and there's no way that I want to be tied to her the rest of my life so another child is out of the question.

So that's where we are now. She's still staying at the house we were renting and I've told her that I'll continue paying the rent but only for as long we're still in this current predicament and then she's on her own and that she should use this time to search for jobs that she can do to become independent. As far as I know, she hasn't had any luck yet although she's had a few interviews to be a receptionist.

It hasn't been a clean cut like I hoped it would be but that's just how things are. We're at a stage where neither of us are sure what's going to happen next.

I apologize in advance for any grammatical/spelling errors. I've just had a long day so I'm feeling a little tired. I'm not sure if I'll update again but this is what's happened since the original post.

TL;DR: I took my daughter and STBXW out to the beach for one last good memory of me. STBXW has been trying to convince me togo back but that's not an option for me anymore.