This must be a tough one for someone teaching himself Japanese as it is studded with slang.
「じわ」: Short for the onomatopoeia 「じわじわ」 = "gradually", "slowly", etc.
「怖」: Short for 「怖い」= "scary"
「スレ」: Short for 「スレッド」 = "thread (in an internet forum)"
So, 「じわ怖スレ」 means "threads that make you feel scared slowly" if that makes sense. The threads are filled with the type of scary stories that get you scared not instantly but rather gradually.
「ビビり」: Slang for "a timid person", "coward", etc. You will encounter the verb form 「ビビる」 (= "to be afraid") even more often.
My rough TL will look like:
"I have become somewhat of a wimp because I often read the じわ怖スレ."
「見る」 can be used to mean "to read".