Not to dwell on semantics, but you are not jealous, you are envious. There IS a difference and it would be good for you to get clarity on that right now for future use. You can read up on that here easily doing searches.
The rules and flow of poly relationships require new skills. Balancing time is one of the biggest ones. You really have no choice but to master this - or bail out and declare poly 'not for you'. It's perfectly doable - lots of us do it, so don't get discouraged. But it IS new so take a deep breath before tackling the learning curve.
Whenever you are involved with someone who has already established a 'life' - patterns of living, maybe involving kids, schedules, commitments etc, it takes some time to restructure all that. Think about your own 'life'. Just keep working at it, making small adjustments when/where possible that move you all towards a place that's as balanced as you can get it. It will never likely be 'equal'. Accept that (everyone). Just strive for the 'best fit' and then decide if that's enough to make you happy. Or not.