How do I say ‘enough’ to lending my mum money?

(TL:DR version at the bottom) I’m going to sound like an awful person I know, but I just don’t know what to do at this point. My mother has never been great with her money; growing up, she was always struggling with high-interest loans and borrowing money from her parents as well as being gifted money from them when things got too much. At one point, she was considering declaring bankruptcy but didn’t (I can’t remember the exact details, I was still pretty young). Being a single parent on an ok-ish paying job must have been so tough. Throughout Uni and my early 20s, my Mum supported me where she could -particularly by not charging me rent when I myself was between jobs and ended up with a hefty sum of debt thanks to a contract I couldn’t get out of and a commute that, together with living expenses I was tied in to for 9+ months, cost me more than I was earning. Years down the line, I’m getting married later this year to the most amazing person. While he earns a lot more than I do, we’re still both paying for the wedding, and I’m still trying to pay off the debt I accumulated whilst out of work with commitments that still had to be paid. I really love my Mum, but our relationship is getting more and more strained. Every month without fail for the past 7+ months, she has asked to borrow money. Some months it’s been like £50, but most it’s been £100-£200. It’s started topping the £300 marks now. The thing is, I don’t have £300 a month spare; I don’t have that much disposable income to spent myself in a month, let alone to lend. It’s coming out of my wedding savings - money I’m going to start needing to pay for things soon. She pays me back each month, but 1-2 weeks into the new month, she’ll be asking me again to borrow the same amount or higher. Every time she messages she ‘feels awful’ and ‘won’t ask again’ if I haven’t responded within 10 minutes of her sending a message (even if it’s when I’m at work), which further guilts me into just giving in when I know I’m already in my overdraft or am going to have to use my savings. Over the holidays alone, I had a long period without a pay check (about six weeks due to how the dates fell) and she borrowed money on three separate occasions despite me highlighting I hadn’t been paid yet. Each time I felt like I couldn’t say no. I know it’s on me too for not trying to say no sooner, but I’m at a loss for what to do. I’ve talked it over with my partner; he’s tried asking if we can just give her some money or ask whether she’s had an unexpected bill she may need help with. He brought it up tactfully last time we saw her, but she dismissed him completely saying her recent MOT was all paid for and nothing to worry about…then less than a week later she’s asking to borrow money because of the thing she just told us was ‘fine and paid for’. I hate that I sound so awful and self-centred, but I can’t help but be disappointed every time we see her. I always end up paying for lunch and she ends up leaving as soon as we’ve eaten; even from when I got engaged, it’s gone from ‘I really want to help you get a dress!” To ‘I want to buy you a veil’ to instead me paying for everything plus a hotel room + other bits for her instead for the wedding. On the other side of things, my OH’s family let us split the bill or pay but always at least offer to have a turn; they’ve offered to help with a couple of bits that aren’t hugely expensive, but it’s 100% the thought that counts (they’ve offered to make things, collect things, etc). When we go to visit them, it doesn’t feel like an excuse to have a meal out - it feels like they want to actually catch up and talk with us. I know my Mum’s had a tough year; her Mother passed away during the last 12 months which was awful. It feels like it’s only further pushed us apart; she didn’t want a funeral or a wake, didn’t want me to come down when she died, and didn’t want me there when she went to pick up her ashes. It feels like I’ve been pushed out completely. My OH suggested maybe she’s having money problems stemming from this, but she always told me she had to top-up the care home (meaning now she’s no longer there, this should be costing her less each month, not more). I don’t know what to say or do without causing further problems. I dread seeing messages from her in my phone now. Every time I make the first contact to ask how she’s doing, it feels like she’s hinting she’s broke (historically, I’ve always been quick to offer to help before she can ask) or now outright asking for money. It’s got to the point where on my birthday, instead of waking up to a message wishing me well, I woke up to a message asking of money. How to I start saying no? How can I/do I try and repair my relationship? I just don’t know what to do. TL/DR version: My mum is borrowing more and more money monthly for the past 7+ months from me. How do I tell her I can’t afford to lend to her anymore without ruining our relationship further?