Aawww mate that's no good
Heres my bit of life experience for you:
Sure he was sad now but why did you break up with him? If you have good reasons then you are probably doing the best thing for yourself. This is one of those times when you can't think about the other person nor be swayed by his emotions. Don't let that part of it make you doubt your decision.
I believe that what is meant to be is meant to be and if you guys are meant to be together then you will find a way to figure it out. If you arent meant to be together then in time both your ex and yourself will find your own happy place in life again.
Its never easy even if you are the breaker upperer lol I know that's not a word. As humans we feel for other people in pain but, I've taken someone back once before who I had dumped because I felt sorry for him and I regretted it about 10 seconds later. Don't go with your heart...go with your gut :) (sometimes its ok to think with your heart but you can't let the heart rule the mind :))
I sure hope things get better for you soon :) chin up :)