So OP, you have a lot of self knowledge and inner resources. If you can access your centre….. acknowledge the panicking part and thank it for trying to keep you safe. Really do that internally. It is a much more effective way of calming it than you trying to push it away. Then find a clam, quiet place with plenty of time to Listen to its concerns. Reassure the panicked part that it is still possible to pull out, and you will listen, but see if it will give you enough space to find your centre, so that you can consider everything with some calm.
The key question here is whether you have a panicking part which always kicks in for any big decision to try to protect you from any mistake…. In which case you need to listen, understand, and reassure it before deciding whether/how to move forward. Or whether your panicking part is highlighting something that is deeply wrong about your boyfriend and relationship and the kind of relationship/commitment that is right for you right now, in which case I would strongly advise you to act on its warning and pull out of the house offer.
you haven’t told us anything objective about your boyfriend or relationship. How does he treat you? Do you feel free to express yourself and do everything and anything you want to? Does he encourage your growth? Does he control you in any way? Does he have a temper? Does he criticise or shout or hit you? Do you fight often? Do you feel respected and safe? Do you look forward to him coming back and are you sorry (or relieved) when he leaves again? Does he pull his weight financially? don’t get me wrong- he can appear to be the most perfect boyfriend in the world and you STILL can pull out because it doesn’t feel right or your instinct is warning you… but if the answer to any of these questions isn’t positive, then you should DEfINITELY pull out.
And then questions about what you want, regardless of him. Do you want to be committed to this area? Do you really love this house? Do you want to be in any long term relationship and live with someone right now? Have you protected yourself financially and legally in the purchase so you cannot lose your investment and can afford to move out/move on if you break up?
The important things I’d say now: 1. Try to find your calm centre - listen to the panic but don’t let it flood you, so you can consider your options. 2. Instincts are very powerful and it is important to listen to them. Unless you have a pattern of extreme, irrational panic through your life, this anxiety is probably telling you something important. 2. You CAN pull out and break up completely. Or you can pull out and stay together. It is ok to pull out, and it is FAR better for everybody to do so before the sale proceeds. It will be much more painful and difficult to reverse afterwards. It will cause more disruption and stress. It will take much longer. And it will cost lots of money too.
This is a really wise time to consider your options before you make your decision. The decision is not yet made and you are not yet tied in.
good luck!