Why did i lose so much sr

i play all the time and i usually gain and lose the same amount of sr. I had some good games and i gained like 5# sr. i played with my friend who is like 100 sr below me maybe even less, we barely lost, and i literally lost 50 sr, srasly pls explain

Unless there is a detailed review of your last few games including stats and the likes, there is no specific answer for you. However there is a really helpful (and huge) guide that explains SR adjustments in general: