Please help...what does this mean from my ex?

My ex and I have been broken up for a little over 6 months now.....we have mainly had no contact except with our birthdays and fathers day we said a few words via email/text........basically i have been missing him since the break up and i know deep down he misses me too....he started dating a new girl withing 2 DAYS of us breaking up from a 5 YEAR relationship :/ ,,,,,It was very hard to deal with at first but i learned to live with it and started dating someone myself....the whole time i have been thinking of my ex here and there while with this other guy...unfortunately this guy turned out to be a scumbag anyways so we broke it off about a week ago. My ex of 5 years just called me yesterday saying he had a "shirt" of mine randomly out of nowhere! I met him at his place and we talked and flirted for about an hour and then i gave him a hug goodbye and its like we couldnt let eachother go. We sat there hugging for about 10 or more minutes and it was really emotional..then we started kissing and after about 5 minutes of that I said we shouldnt be doing this and he said "omg im so sorry i did that, please never tell anyone, i am very happy with the girl im with, im happy that it happened kind of because now we know that nothings there"...and i sat there dumbfounded because if nothings there how could you hug me like that for that long and kiss, etc. He made me promise 100 times not to tell because he didnt want to lose the girl he was with for the past 6 months since our breakup. I agreed because i dont want to hurt him or ruin his happiness if he is happy...now im sitting here depressed just like the breakup that happened 6 months ago! What do i do and what should i think of this situation? Of course, I am going to leave him alone and continue no contact i guess but do you think we will work out in the future after their honeymoon stage is over?