Why is this happening to me
Welcome here to the Forum, its a place where many people are unsure of the way they feel, almost like there is some 'proper' way to feel and they are failing becuse they feel differently.
People fall in love for lots of reasons, does not have to be good looks or anything like that, nor even love by the other. It happens when you are ready, not at a convenient time. As you said, your heart has been broken twice - 2 years ago, a week ago.
It simply takes time to heal, and a heart can take a very long time. I'm not suggesting you break up with your BF, you do not know what will happen, and I'm sure you can put things in a way he can understand and are not hurtful. Maybe he will want to stick around even knowing how hurt you have been.
Relax (as much as you can) and enjoy the company, hopefully you will good company for him too. See what happens.
You mentioned you have BPD, OCD, depression and anxiety, a combination sure to fill one's head with negative and questioning thoughts an awful lot. May I ask if you might consider finding medical support that does help? ATM most people can have tele-health consultations. You are the expert on how you are, you are in charge, and need to find the combination of support that clicks.
I never improved until I had the right GP and psych.
Do you think this might be worth doing? If you did and wanted to discuss how that could be in another post.
I look forward to hearing from you
OK so you now have a very good freind htat seems to tick all hte boxes, but you don't respond inside. Maybe that is because you are not yet ready to plunge into love - and risk yourself. Oh yes, love is a risk, and you have been talking about just that .
No apology needed, you reply when it is the right time. All good.
After a number of malign boyfriends I'm not surprised at all your heart keeps things in reserve.
I guess it is a measure of your perception that you had realized history was repeating itself and it came down to making choices. It sounds like you have made a good one this time. To have that perception would seem to me to show you are moving out of a loop and into fresh ground.
Maybe you need time.
As for animals, not only does my family have an endless steam of rescues, Sumo Cat and Foxy Dog at the moment. Until we were no longer in a position to do so we had orphaned wallabies (from roadkill) in bags hanging in various places and later bounding around making a right mess.
You don't really know what is impossible, do you? It is certain you can love when things are right.