is this nipple confusion/preference or just baby adjusting

i just went back to work, two shifts a week and i’m roughly gone around 5 hours each night. baby is 9 weeks old tomorrow and since i wanna say about sunday he has been eating in smaller increments. he’ll eat for maybe 5-8 mins every hour which i thought maybe cluster feeding? but he’ll down a 3 oz bottle while i’m gone. we ebf for the first i wanna say 4 weeks and slowly incorporated bottles to help him adjust early, hoping it would help. but now i’m scared i’ve done something wrong and he’s not eating enough from me. i don’t want our breastfed journey to end so soon it’s making me sad. but obviously i just want him to eat in the long run. what can i do to fix this? is he just adjusting to me being gone and having more bottles? thank you