ex's perfume​ on boyfriends draws

okay so my partner had gone to work and his room was a mess so me being a clean freak cleaned his room so he wouldn't have to do it after a stressful week at work ... while cleaning his draws I came across some perfume. I asked his mom if it happened to be hers and the response was 'no love it's not mine. its probably his ex's'... we have been together for 16 months and I've always taken things like that with a pinch of salt . I just wonder why after nearly 2 years of them splitting up he still has it .