Josh be serious chase thought he did it with a dog in what world is that better than doing...

Idk how Chase and Josh ended up having sex, but considering how emotionally centered Chase is, knowing that in the past he possibly r-worded the person he loves and ended up getting Josh pregnant would certainly mess with him. Also, Chase is surrounded by opportunistic people most of the time, knowing Josh had his child and had a mark from him but still hid it till their relationship progressed to this extent may also fuel his trust issues.