Now I'm pretty certain that Michael didn't kill himself after watching it again. It wasn't a chest shot or anything, it was angled.

So why would he have done all that?

Maybe the Others brainwashed him in some way but I don't think so cause you could tell he wasn't happy about doing it. Or it was some kind of a deal to get Walt back. Or maybe it was a way to get everybody angry and willing to fight the Others. But I don't think its that cause Ana already told him that they were getting the guns to go after the Others. So I think its some kind of a deal for Walt.

Which makes me think that Mike was full of shit when he said that the Others weren't that strong

Also Michael didn't come back with his gun, at least I didn't see it.