Hey @Turtleshell. I understand what you're saying in a lot of ways. I don't know how old you are but I was like this until about 18 months ago and i'm 53 now. So I don't think it's ever too late. Reaching out here and sharing your story is a fantastic step and very similar how I started to work on my own issues.
No, you're not an alien. There's a lot of people here who will identify with a lot of what you wrote. Plus many, many more out there in the community.
When I saw a psychologist for the first time, she asked what I hoped to get out of it. My answer was to be more open and better at letting people close to me because, like you, I had a partner and I had the same fears as you. I wanted to improve so I could be better for her because I thought she deserved better and it was only a matter of time before she realised. I did get better at talking to her and letter her know what I was dealing with. Not good at it mind you, but better. I found my trust in her grew because I found out that she wanted to support me as much as she could and was had far my faith in me than I did.
I know it seems impossible at the moment... God I felt that way for decades! But it's like we tell ourselves that over and over again until it just sort of becomes fact. It's not impossible but it is hard and it wont change overnight. You just need to chip away at it. After all it's chipped away at you for many years so it will take a while to repair all that self-damage.
I've found just talking to people on places like this, or support groups has given me connections to people which has helped me to realise I am worth something and people can like me. It's still difficult and I still need to remind myself of this quite a lot, but like I said it's only been about 18 months and the low self esteem has been chipping away at me for most of my life so naturally it's going to take time.
So basically my advice is to keep doing what you're doing but stick with it. Start off by just getting to know people here. Something I made myself do was to make sure I relied to anyone that replied to me. That got me in the habit of interacting WAY more than I would have normally done. Then read other people's posts and offer them some support or just tell them how much you identify with what they wrote if they talked about being lonely for example. Then try to build that into more face to face connections, like support groups or social groups... anything in your area that you think you can handle. It's just a case of building slowly, pushing yourself, but always trying to build more connections. Hopefully you'll soon start to doubt all those negative thoughts you've convinced yourself were true and you'll start to feel more confident and like you can make and keep friends.
I'll leave the choice of medications or not to you and what you think is best. I've had them recommended to me a few times but I just have my doubts. I haven't had any experience with them (good or bad) but I just have my doubts so I don't want to take them, but that's just me. I've heard from some people who swear by them so it's up to you if you're willing to try them again.
I wish you all the best. I know how so well how damn hard it is... mentally, physically, and emotionally! It sucks. Me from 18 months ago would have never written any of this, or any of what you wrote, but most days now I have contact with different people and get support, give support, and have a laugh as well. Even if some of it is through a keyboard.
So have faith in yourself, have faith in your partner and always try to share your struggle with them. After all, would you do everything you could to help and support them if roles were reversed? That's the way I try to look at it with my partner.
I wish you the best of luck. You're not an alien and you're not alone. We're here to support you and get you to a more positive place.