Don't worry - first of all it WILL get better. Probably really annoying to hear that, but it will...
Try and establish a routine where you get an hour to yourself each morning but 'are still there'. By this, I mean after breakfast, put ds into his cot or playpen with some toys. He may scream, but just smile and say Mummy's here and then potter about around him tidying. I did this and it was difficult at first but now ds(2) is very happy and it allows me to get showered and clean up all the breakfast stuff. I will sing to him and always pop my head in the living room every 10mins or so to let him know I am there.
In this same hour slot, can you give dd some chores at weekends. So, you get showered and she tidies up? Gives her some responsibility and helps you...
So, that's an hour in the morning sorted.
Then in the afternoon I do find even though it's a pita go out rather than stay in. Soft play for ds as his screams will 'mingle in' and no one will even notice. DD could read/have lunch with you/go on an ipad/or could she take a friend to soft play for a chat or play - do 9 year olds still like soft play?
Walks -again, it doesn't matter if he screams his head off - just keep pushing the buggy and you can take dd to the shops to choose a treat or help you get stuff for dinner.
Swimming - dd goes in alone (or with a friend) and you go in with ds.
Library - dd gets to choose her books and ds plays on the floor
Zoo/parks - both entertained.
I presume it's the weekends are the hardest as in the week dd is at school.
Is there a creche at the leisure centre you could put ds in (if you feel comfortable?) Could you find a childminder for a couple of hours at the weekend for ds? Give these people (Home Start) a call - they are amazing - www.home-start.org.uk/
It sounds like you are the doing the right thing -keep going as you do have to get out and eventually ds will get used to it.
What's the bedtime routine like? Can you get them down within an hour of each other so then you have time at night for you. What about setting up playdates with dd's friends so then it is just you and ds for a bit.
I don't have any experience of big age gaps but am sure plenty of helpful mn'etters will be along that do, but I would try and get the older one to help as much as can as she is not a baby and that would be a huge advantage.
Also, when ds goes to bed that is your chance to spend quality time with her just the two of you, and thank her for being such a wonderful big, grown up sister!
Maybe, contact a HV and have a look on amazon for any helpful books. Also, DH will need to have them for a couple of hours on his day off so at least you get some time alone - he may be tired, but that's life!
Re:weaning, speak to the HV, go onto this site www.babyledweaning.com or post here in the weaning section.
Re: friends - if you take ds to groups you will make some, it's just finding the locals one that you like.
Good luck xx