I know how you feel. I'm not that experienced in agent rejection compared to many - I've only had about a dozen rejections over two books so far. I have writer friends whose rejections run into the hundreds. All I can say is to make it easier on yourself, only send out when you're really ready. You'll think you're ready, then go polish your subbing package some more. I've sent out material that wasn't as good as it could be and it was, of course, rejected. With this latest novel I've rewritten and rewritten, been very careful about supporting material (cover letter, synopsis) and I've had two very positive, helpful rejections and a full request. Good luck with it all - you're in the right place to succeed.