from what ive seen in my years, this is just a gut feeling: bc it happens to many people. but im gonna guess it goes beyond fantasy football
i dont know you or your life so forgive the assumptions...but ive noticed a trend with people similar to your case. that fantasy is like a way for them to prove themselves...potentially dont have much else going for them- but if they can at least win in fantasy- hey thats great right - not to mention if people have way more time on their hands arent as social maybe between jobs they can easily get sucked into investing tons of time - and if a loss happens its like that time feels all for nothing

heres the thing though- you said its with a group of friends - i too play with a group of friends...for 13 years now. if somebody goes 2-11 (for ex) ive never in my life noticed them suddenly be less accepted by the group...like the guy is still our buddy. we might make the potential jab at his horrible fantasy year- but sometimes you just gotta shrug it off- or embrace badbeats in a 'lol - another bad loss..as is tradition with me...o well'
people that are really secure and dont seek approval tend to be far less depressed by losses. i dont mean this as an attack but im only saying it bc ive noticed the monster common trait between people that take fantasy losses so seriously is when they feel like they need to prove something. gain the respect...ultimately these are your close friends
its not like youre trying to impress a group of strangers at a work office and maybe if you do well they think highly of you in the office maybe even ask your advice on things- great feeling to have
but i mean these are your friends

think about it this way- i dont know you but ill speak for myself - growing up me and my friends were highly active- would play scrimmage games in all sports- backyard bball games...football at some park in the area...it was competitive no doubt- and yeh sure it sucked to lose- but its not like that would ruin anyones day...its a game among friends

and lastly- if its financially related - the stress would likely be caused if youre in a tough financial situation and just cant stand the thought of losing ur entry fee or u realllly wanted that prize. if so - then you gotta do whats financially smart for yourself

but ultimately i dont think this has anything to do with fantasy- but rather other issues that have a bandaid on them and the losses in fantasy are bringing them out. hyper obsessive caring about whether your team won or lost points to larger issues.

do things that make you happy -sounds like you have a nice group of friends. you got a girl that hopefully its going well- focus on the positives my man. losses happen. its easy to lose sanity thinking of what ifs...jsut gotta look forward and stress a bit less. find other things to occupy your time if you must.

and if a lost happens so be it- your friends might shittalk- but i doubt anyone loses a friendship bc they lost in a fantasy game lol...like theyre still your friend.