All over the place...

My husband and I have been together for 15 years, married 11. Over the past 3-4 years we have had major issues. For a brief outline:
Approx 4 years ago he messed around on me at my friends party while I was out of the country
Approx 2 years ago I developed feelings for one of his friends
Last year he distanced himself from me and felt unsure about our relationship
This year recently, he had been visiting online chat rooms and exposed himself to women/had online "experiences"
We have had an active sex life including fantasies being fulfilled (3ways included).
He has been bugging for another and I am not ok with it anymore (he distanced himself after the last one) and it is just not as exciting.
This is when he then started the online thing.
He stated he doesn't trust me and that he isn't into sex as much.
I confused as obviously he seems to be...
He is depressed and is suffering low esteem. He says he can't get it up as easily and although he watches porn, he's not overly interested (I don't really know if that is true or not).
It bothers me because I feel like he's not into me. I have not physically changed or anything, so he has no "reason" to not be attracted to me - but I don't know if he is.
We have been trying to work on things and spend more quality time together to rekindle our love. I think we are both bored. But not just with sex, just in general. I wanting to be optimistic and work on it - what can I do to make it better? What is a fun guy date? What will impress him? How can I get him to do the same for me?
He has said he doesn't want me to leave, he wants to work it out and that he loves me. And has "begged" me to stay. I guess I'm just feeling hopeless and unsure in his sincerity. Regardless, we have alot of history and I want to do everything possible to try and make it work. Suggestions?