OP, who is the primary carer for the children? Are you a SAHM? If you both work, who collects the children from school, feeds them, listens to them read, gets their book bags ready, etc, etc, etc? If you and your husband do this equally, he could make a case for 50:50. If you don't, he can't.
People assume a parent can just demand 50:50, but that isn't how it works. The way it works is that the children's lives are to be kept as 'normal' as possible, given that they are in a scary, new, shitty situation as a result of divorce. So if one parent has largely been absent (at work, pursuing hobbies, having 'me time' - whatever), then that parent will see correspondingly less of the children.
I am not going to tell you what to do, OP, as I stayed in order to make sure the children were with me all the time, and I know this goes down badly on MN. But I really strongly suggest you tell someone IRL (doesn't have to be the police or Women's Aid, if those things feel too big). Your mum, sister, friend - anyone you trust, and who isn't related to your husband (so not his sister, say, if he had one and you got on well with her). Then take it from there.