I'm pretty sure that guy is Tyreese, because the showrunner said he'd be showing up soon and I read somewhere else it was in the midseason finale.
I also think Daryl will kill Merle, because Merle will attack Rick for what happened in Atlanta, and Daryl will have to make the choice between the two.
... And who wouldn't go for the Governor? I mean a) he's interested in Andrea b) he could be worse looking c) he's single d) choice is limited e) he treats her okay and f) he's offered lots of people a kind of stability/sanctuary and some people find the whole leadership thing attractive. I completely understand it basically. I'd probably feel a lot different if it was like... Negan she was attracted to