Is this allowed or considered nesting?

Good evening--

I need to be in the USA for an extended period early next year but will be flying back to the UK (London) every few weeks.

Am I permitted to book a roundtrip with a 6 month stay (depart jan return June) and book round trips in the middle of that ticket? The reason I cant book keep booking seperate tickets in advance is because i wont know my work schedule until I get to the US and that will dictate when I fly back home to London then back to LA.

Thank you for you insight.