How do I tell if I'm unintentionally using someone?

Okay, so some context. I(24F) got into a relationship with a friend (25F) about a month ago. I was told by her sister (ain't that just the cutest?) that it was coming and so I had time to think it over. She's sweet, if a bit needier than I normally go for and we got on well as friends. We even lived together for a while and had a lovely time. So, why hesitation?

I was worried about 2 things while weighing my answer. 1. that because she is both attentive and needy, we may be incompatible outside of friendship (in friendship, I can regularly recharge and she would be less dependent on me, as I.. struggle with emotion and tend to feel manipulated and on edge when people want to be close to me or cling. working on it in therapy.) and 2. I've been on and off again in love with my best friend(24NB) since we were teenagers. I've resolved to never do anything about it, since I'm in their life for however long we have no matter the nature of our relationship and it's honestly enough. But it always makes me worried when dating.

So. The problems. My girlfriend has been lovely. I like getting her things I think she'll like and seeing her in the little things around the city. I like being close to her. She's a little more handsy than I prefer and I'm planning on brining it up gently soon, which I'm sure will go fine. It was something I told her about before we were dating. All was well.

But I didn't want to tell my best friend. Normally, I don't like my friends meeting each other anyways (group hangouts suck lowkey highkey), so it isn't much of a surprise, but. I don't like it this time. It feels sh*tty. And I can't tell if I don't want to tell them because of my usual reservations against sharing big life things and the ensuing questions or because there's a part of me that still hopes they're in love with me too. I'm less inclined to think it's the latter because it's an open relationship and if I wanted to date my best friend too, I would just need to let my girlfriend know in advance for STD and STI reasons. Also I straight up told my girlfriend about being in love with my best friend. But how would I know for sure? And how much of my panic and moralizing is real and how much of it is my OCD?

And then. My mother started dying. Is dying, it'll be.. a long process. She's been ready for a while, and it shouldn't come as a shock. Doesn't make it easier. She's the only good family I have. And my best friend has been through the same thing with their grandmother, who raised them. So. I went to them for advice.

The first few times I mentioned I was grieving to my girlfriend she was... a bit dismissive? Not intentionally, I don't think. It was just. She'd ask how my day was, I'd say a sentence or two about how I was honestly, she'd pat my back, and then. The conversation moved on. Very... no bummers kinda vibe, right back to games or work. Which is understanable, my mom is not capital G gone yet and she's been sick lately herself and what do you even do, right?

But the past week it's changed? Kinda suddenly. She doesn't want to go out or do things out of worry she won't be there when I need her. And it's at a weird time, when I'm... almost doing better? I've been to grief support and rehab before so I kinda know the ropes even though it's a whole different kind of grief, mourning someone who's alive. But I'm... at the top of the wave right now. There'll be more waves, I'm still in the sea and will be swept into the undertow again soon, but I'm okay right now. Which I let her know. I don't think it helped. I can't tell if the rapid switch made me uncomfortable or her suddenly pressing when I didn't need or want it made it feel like prying, but either way. It's... been making me nervous.

She's also getting more serious. We've been friends for a while, so it's not surprising, especially when she's had feelings for a while, but. I'm still in the figuring things out stage with her and I don't know how to tell her that without hurting her.

All this is to say, it feels like with my hesitance to bring her up to my friends, her getting serious when I'm not there yet, and the...mixed support messages I can't tell if this is a relationship I want or if it's just my anti-attachment shit going off making me question things or if it's me using her as a replacement for my best friend secretly or something.

Any advice on how to tell, how to test myself? How to sort out thoughts? Ect? Lmao