Op, you sound tired and fed up.
I've just come through a period of about 6 months of going to my full time job on about 3 or 4 hours broken sleep each night.
I'm also still breastfeeding and we have zero family support, nil, nada, zilch, niente, nothing. I drop my baby at nursery and do the school run for the older two. Their school is right by my work so I don't even get a minute to just relax in the car.
Then I go to work which is a full on, people facing, work-through-your-lunchbreak kind of job, collect the kids, make dinner, do homework, activities, washing, iron uniforms, do lunches then up all night with the baby and rinse and repeat.
Myself and my husband divide the jobs but the place is always a mess, I'm always dropping the ball somewhere and the only time I get any alone time is when I'm on the toilet or having a shower, and even that is fleeting as we lost the bathroom door key.
I used to get so annoyed when people who worked part time complained, especially if they had fewer kids than me. The thing is, everyone's hardships and challenges are different. You need to do what you can to free up some emotional space and get a break. This is what's making you feel so bitter, and as a result, you can't see the wood for the trees. Your intense days qith a young child will pass, but your friend will forever be separated from the father of her child (probably) and even if she meets someone else, there's a level of complexity that will be in her life that you don't understand (me neither actually!).
The fact that you are jealous of a situation that nobody would choose for themselves, suggests that you're feeling desperate. I'm sorry if my first post came across as judgemental or harsh. I think you need to sort out whatever is making you so burnt out so that you won't feel envious of less than ideal situations. If you feel like you are losing yourself, take action. Hope all goes well.