I don't think you're a coward. You're being kind of cowardly but you're not a coward.

If it were me, I'd just keep pretending nothing was wrong but nothing's going to get better unless you say something, you know. It's not. You're just postponing that inevitable point where the realization hits and everyone gets upset. You should just tell them soon otherwise it'll just eat at your insides like it is right now and then when they finally find out they'll probably get way more upset because it was kept from them.