It sounds like you're in a rough spot right now. Try to just breath deep and know it will eventually pass, even if it doesn't feel that way right now.
I do find it helpful to keep the baby in the sling as constantly as you can. This way you're giving the baby your attention but to your toddler's eyes you're not as focused on the baby. It's kind of like being pregnant from the outside. It's easier for the toddler to accept and you can tend to them more easily this way. Also, like a PP said, you can nurse out of one side while the baby's in the sling (the breast under the rings) and Eli can just stand to nurse or sit up beside you. Also, can you nurse lying on your back (with them each cradled in one arm)? Another good one is nursing the baby while side lying and letting Eli straddle your hip and nurse off the other side. I know you want to get up, I'm just thinking if you need to relax these are good ways to do that while nursing.
Also, he'll want to nurse less while you're out and if you can keep from sitting down while you're home. If you can nurse the baby in the sling (especially with an open tail sling you can cover her) he won't know she's nursing so at that moment he won't need to, kwim? Are you able to get out and go to the park, library storytime, playdates, etc.? I would try to keep him really occupied if you can but still try to nurse him when he asks. If he senses you're not wanting to nurse him he's going to want it all the more. Also, if he does need to wait (you're going to the bathroom, you're in the middle of something etc.) just let him know he can have booba as soon as you're done doing X. Then as soon as you're done follow up and nurse him and tell him thank you for waiting, you know it was hard for him. I know, that is so hard to hear them scream. I think this is just one of those places a lot of mothers find themselves adjusting to two children and the siblings adjusting to eachother - whether you're nursing them both or not.
I hope this improves soon.
* I wanted to add a couple of things. Have you read "Adventures in Tandem Nursing?" Also, here are some things that many mothers have found helpful when an older sibling is having a hard time adjusting to the new baby:
- try to involve him in "helping" with the baby (have him bring you a diaper, a toy for the baby, let him lift up her side of the shirt to nurse, if she cries let him gentle "pet" her head to help her feel better, etc.)
- try to comment on what a helpful, kind, special big brother he is. Point out when the baby likes something he's doing. Try to "talk" to the baby about how lucky she is to have such a wonderful big brother (so he can hear you).
- Try to have dh or someone else hold the baby while you can read a story to Eli or do something else that he likes to do with you.