First off, I'm so sorry you find yourself in this situation. None of it is fair. None of it easy. Take some solace in knowing you're being a good person and a good dad.
Regarding the finances, if she's able-bodied, she should be looking for work or going back to school. What does your lawyer say about alimony and getting her to cover her expenses?
As for making friends, I've found the best way is to regularly get together with the same people. Clubs are really good for that (book club, hiking club, sports club, etc.). After a while, you start to get to know people, and you'll figure out who you click with. Then invite them out for something fun, or invite them to your house for pizza and a movie.
I used to work three jobs and had a kid, and after I discovered my stbx's cheating, I was desperate to reconnect with people and have people I could talk to and trust. I was also disabled at that point, so I couldn't go out much, so instead I started doing regular zoom meetings with people, like once a month. It was a great way to form new friendships, and there are a few people that I still "meet with" online every month or so. I also joined a local book club who meets monthly, and that's been great too.
All this happened when I was in my late 40s. You have time, and with your kids being older, it'll get easier. You just have to make it a priority to carve out a few hours each week for yourself.