What does it mean , and what should I do

So my ex / baby daddy moved in with some chick a few days after we broke up .he works with me bust hasn't showed in 3 weeks . he hasn't talked to me in 3 weeks and ive messaged him 2 times already to give me back my shirt and glasses he reads it but doesn't reply , I really want it back and no not to see him I told him to leave at my front door when I was at my other job but never replied . I'm now just getting pissed idk what to do it's my fav shirt and it's from my dad who lives very far away from me so it has sentimental value . Why do you think he's doing this , and what should I do