Spending time with animals like you've been doing is a good call, and you should keep it up if you can. Since you can't buy your own pet, you could try to volunteer at sanctuaries/shelters or visit pet cafes.
You also don't have to specifically get an intelligent creature. There are a lot of low-maintenance or more unintelligent pets, like a small lizard, or even plants. Gardening can have positive effects on one's mental health.
This may sound stupid, but you could also look into playing romcom visual novels/dating simulators, or reading romance novels. A lot of them are made specifically for wholesome stories and feel-good romance. Yes, it is escapism and seen as pathetic by some, but so long as you keep a healthy distance and keep in mind that it's fiction, it can be nice to immerse yourself in one.
I also think that finding a small online community you fit into, other than SaSu, would help a lot. SaSu is not good for oxytocin. It is mostly filled with gloom, misery and death. I understand that this is daunting and difficult for you, though, so it's just something to keep an eye out for.
Depending on where you live, you might be able to purchase oxytocin supplements. I'd use this as a last resort, though, since it's always better to do it 'naturally' as opposed to relying on ingesting concentrated hormone in pill form.
No matter what, though, friendships will always be the best way to do this. You don't have to go seeking one out-- it's better to have no company than bad company-- but don't isolate yourself, if you can help it. You don't need to trust any strangers from the get-go; just having small talk or engaging in a small activity with someone is a perfect place to start.
I wish you the best.
