Is it normal for me to feel so weird and jealous after reading two intimate love poems my boyfriend wrote ex?

I was at a friends house and this friend has been a friend of my boyfriend way longer than I've known him. Me and my boyfriend have been dating for 2 and a half years. My boyfriend is a talented slam poet and writes wonderful poems. I guess before I knew him he left a notebook of his poems in the bookshelf of my friends house and I saw them and wanted to see what his old work was like. I ended up finding 2 very intimate poems about his ex ...like describing how they made love and were perfect for each other with all of these suggestive metaphors. I trust my boyfriend but for the rest of the day I felt sorta gross and jealous. I mentioned that I read those to him and then was really embarrassed for saying anything at all.. I guess there was no point in me mentioning them.. it sorta ruined our night of hanging out by how weird I was felt. I know it was in the past before he met me but I just cant get those words out of my head... its my fault for continuing to read the poems even though I knew they were about his ex I guess. Has anything like this happened to you? Is it weird to feel jealous ? p.s he is my first boyfriend and first guy I've ever been physical with.. could this be why I cant relate to him having an ex and am so weirded out?