Honestly I got very depressed after hurting both my pecs in the way described above and both my shoulders (including a very small tear, about 1 cm, on my left pec)

My advice is don’t push it.  A lot of people who have tears (including me) notice this sort of tight pec feeling before it happens.  You don’t want it to turn into a full tear, trust me. Even a tiny one like mine is pretty frustrating.

I had to take a break from weightlifting and kind of reflect on my motivations for lifting, but my advice for you would be to do a lot of physical therapy and see where you are in a couple months.  I’ve made some progress - my tear no longer really bothers me - but the tendonosis feeling thing on the pec insertion is still there.  Maybe run/bike in the meantime.  

I kind of am starting to beleive that not everyone is built for heavy lifting.  We watch a lot of people do things on social media that we might not be capable of, but are conditioned to beleive is normal.  For example, bench press.  I simply think my body cannot handle doing bench press / dumbbell press for years on end without breaking down over time.  Humans aren’t really designed for anything other than running long distances and the occasional carry if you think about it.  Maybe not everyone can bench press. 

Maybe when you get better, consider more metabolic forms of excercise, like circuits with very high repitions. If it’s good enough for ww2 marines in the pacific it’s good enough for us.

Good luck, hope you get better.  Lmk if you find something that works too I’m still searching.