Hi!
I deal with regret and depression every day. I lost my relationship with my daughter in January due to her stealing, drugs, and lying. My dog just died. My adoptive parents abused me. So did my husbands. So, I kinduv know how you feel.
What has been working for me (aside from med changes) is reaching out to people...like you just did! Just keep reaching out. Hit the boards every day. Take strength where you can find it.
And, my saving grace is that I developed an all-consuming passion for something new. In my case, it was Battlestar Galactica. It's the story of how people survive after their lives get nuked. (Which was how I felt in Jan.) Obsessive veiwing, and hooking up with some really great people on those boards saved my butt!!! And I'm not even a big SciFi nut.
Your passion will probably be something entirely different. But, you will probably have to force yourself to get super involved with something outside your life (like I did - I'm a hermit). Getting outside yourself really helps. Still...I don't know of anything that can ease the pain of loosing a beloved pet. In my case, one of our other dogs has suddenly adopted me and it helps. You have my deepest sympathy on all your losses. And my support.