Weird that I got jealous/ mad.

So my boyfriend and I started a long distance relationship and he gave me a T-shirt to wear of his when I sleep. I was looking through some of his Facebook pics bc I miss him and I saw an old picture of my bf and his ex. She was wearing the shirt he gave me in his bed. Idk why but made me mad/jealous that he gave me the same shirt he would give to his ex. I did say anything to him of course bc I’ll get over it. but it does bother me and make me feel some type of way that he would give me the same shirt he gave his ex.