I guess I can't be much help because I don't have any first or even third person experience for this kind of anxiety and panic.
I wish it could be as simple as just having a certain mental focus and then doing your best to believe it. I would love to say that while we have all been through damaging break ups, but we have to get back on our feet to keep trying, to completely write off the other sex and want to curl up in a hole would not be a proper way to find somebody and all you have to do is keep looking and you will find Mr. Right. Etc. etc.
I know you can't help how you feel or you react so it's a tricky situation.
We all make mistakes but our failed relationships should make us stronger people and not weaker. It should be a learning experience so that you can make better decisions on which guys are right for you and which ones are not. You aren't a helpless person, and possibly your damaging relationship has made you feel that way or like a victim possibly? You can just as well stand your own, trust your gut instincts on things, and if you aren't happy get the hell out. Don't put yourself in a mindset where you are going to self destruct something before it happens, it's left me pretty inept.
You are only temping, you are gone at the end of the week and he is no longer your boss. Unless you are moving far away, I think this is a great opportunity. Before the end of the week, find a way to keep contact with him afterwards (email, phone number, etc.). That should be a pretty blatant way to let him know you are interested and you will know if he is based on reciprocation.
Take the time to get to know him, take it slow, get a feel for him. A good guy won't expect too much right away and have lots of stuff on his own plate to occupy his time. And he will understand you may need some time to open up and won't pressure you. You don't have anything to lose do you?
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.