I completely agree with PPs that these things come in waves. Your time will come OP! I was you 6 years ago - divorcing, left a crap relationship, single mother living in a flat with DS. Both DS and I suffering from poor mental health. I'm highly educated, but worked in a fairly lowly paid role, whilst everyone around me had careers, husbands, lovely children, big houses.
6 years on I've met my partner, have a better job, just in the process of applying for an even better one, we are comfortably off and have a lovely 4 bed that we are renovating. I'm sure in a few years we will hit another bad patch too, as some of my previously successful friends are unfortunately facing now.
Everyone has crap times, it just seems like when yours comes along everyone else's good points are magnified.
Be kind to yourself, know that things will get better and take time to look after your mental health. It's so hard to see the opportunities when your mental health is suffering. Get that sorted and I am sure you will start to see other things opening up.
Your friends sound nice (like mine are), it's ok to let them know you just need a rant, no advice necessary. I'm sure they will understand. 💐