10 years is a lot to throw away. I'm just going to put my opinion out there and you can take it or leave it.

A relationship will have their ups and downs. Then they may have those times like this. At 10years together and your practically "husband" (10 years is like a marriage maybe not on paper but by the love it took to last 10years) opened up and told you how he was feeling. You are the one that walked out and left to stay else where. After being that long together there are BOUND to be times when feelings fluctuate. The fact the he asked you to come home to talk is at least some proof for you that he isn't wanting to just end this. To me though it's quite a lot.
"He said that he feels like he doesn't make me happy." A man that loves you wants too see you happy and HE may be HURT inside that he feels he fails at this. You can't sit here and tell me that after 10years and him being with you through it all that he hasn't made "a depressed person" happy. Doesn't he deserves some credit? Which maybe he was reaching out trying to get from you?

You say you won't beg, and maybe he was looking for a show that you wanted to stay. After 10 years with this man that I can almost assume has treated you well and been there for you through everything by reading your words that maybe he has a right to want to see that from you. How can you be so stubborn to hide those feeling from him despite the clear loyalty that has been shown?

I'm not saying you are in the wrong, but from reading your text, he is not either. He should feel open in discussing his emotions as well and as his wife/girlfriend or what you consider yourself after a decad should be there to help HIM feel better just as has for you over the many years together.

You should be there right now kissing him and telling him the love you really do have for him because it appears to me he was searching for some kind of reassurance. Men have feelings to, even without a MI people can feel depression, they can feel worthless and not enough. Maybe, just maybe it's your turn to help him realize and understand the true deep love you have for him and be there for him.

Don't try to fool yourself and think it's not your place to make him feel better because we are not talking a 1year relationship here. We are talking a DECADE with this man... It's become your place years ago.

You throw this away as easy as you are and you may highly regret it one day. The man thats been there through it all, held your hand through good and bad, showed you love and loyalty for 10 years IS WORTH FIGHTING FOR!

Men like this don't just come around and they are very rare. If he says he doesn't feel the same, make him remember why he fell in love with you. It's work yes, but anything worth your time and love will always take work. But it's damn worth it.