My sister and I were best friends growing up. In the past couple of years, she has met, dated, and married a guy with mental health problems that affect their day to day life. My sister didn't know the extent of his problems until after they were married (and to be fair- I don't think my BIL even knew how much he’d struggle).
The outcome is that my BIL requires regular reassurance and support. He struggles with crowds. He says he can't work (which was not the pre-wedding plan) so my sister works to support them both. He manages some minor cooking and cleaning in the house but the bulk of the household work is my sisters, including dealing with phone calls, bills, etc.
As a result, my sister’s money and time is tight. She is always looking exhausted when I see her. I feel sorry for her, equally, she knew at least half of his issues when she was getting to know him, so she has willingly taken on a lot of this.
My problem is that now my relationship with my sister has completely changed. We have not spent any time just the two of us since the wedding (though I have asked). Whenever we do something with BIL and friends I often have to offer to pay for the activity because my sister can't afford it. I have tried to spend time with BIL at least a couple of times a month when I get a workday with an early finish and my sister is still out working. I have given BIL lifts in my car as he doesn't drive. But I'm now starting to feel like an assistant rather than a sibling.
The final nail in the coffin so to speak was just recently. My BIL and sister’s 2nd anniversary. I gave them money in a card. (I knew they wanted money over a personal gift). It was more money than I could reasonably afford, and it was on top of constant purchases mentioned previously (which I'd made with the intention of helping my sister see our friends as otherwise, she might decline their invites out). They did say thank you as I handed them the card. But it sounded like the same thank you you might say to anyone passing you an item. And after that I received nothing. I almost wonder if they had expected more money and were disappointed, or if they were happy and just didn't bother to text to say thanks when they opened the card.
And for their anniversary they were able to go on their first holiday abroad of the year. I don't begrudge my sister this - she needs a break! But I haven't had a holiday abroad this year because my funds are so tight and I started remembering all the times I must have paid for their stuff while they were saving for this trip. It made me realise I'd helped them way too much. And been taken somewhat for granted for it.
They have a new kitten and asked me to care for it for 3 days. They said cats don't need a lot of attention so, to be honest, I was expecting to drop in maybe twice a day and sort food and water and maybe play with the cat for an hour. Turns out kittens are not supposed to be left alone for more than a few hours (discovered via a friend and then internet). So I have had to reschedule tons of my diary over these 3 days to feel like this kitten isn't going to be left emotionally wrecked with loneliness or do damage to itself. It's surprisingly exhausting - the kitten barely sleeps during the day and I've just discovered that the friend who is going to be house sitting and cat sitting for them when the 3 days is up is actually coming late into day 4, so I'm still going to have to get over there and care for the kitten on day 4 too.
In short - I feel like my sister is worn out and I am just a crutch in her life now. We don't have any private chats, I only see her with friends when I've offered to fund it, and anything I do for her she doesn't seem grateful for. How can I address this with my sister to repair our relationship? I know with BIL it will never be truly the same, but I want it to be functioning. She has no idea how I am or if I need help. What can I say or do to try to reassemble this relationship?