Not a guy, but it sounds to me like he loves the rush of new love (the giddy insanity of that first flush) and once that is over and when the real deepening love starts, he goes searching for that buzz again.
Some non-alcoholics are hooked on this too.. so jury is out on whether it's anything to do with the addictive side of his personality.
Put that aside though, because that's him and it is his stuff to deal with. Sounds to me like the push/pull doesn't work for you.. so you are left with a friendship. And as in any friendship, you can voice an opinion but what they do with that is up to them. You may feel the reasons he has given for pursuing this relationship are the wrong reasons.. but they're his reasons.. and the consequences will be his if it fails.
Tx