I find that getting involved with other players or like a guild can really help you stick to a class. The reason I say this is because my boyfriend had the same problem with not knowing what to play because he liked so many classes, but after he ended up joining a guild and he found a spot there and they depended on him, he finally was able to stick to one without too much trouble.
Sure the options are still there for him, but his main focus is now on his guild and friends rather than trying to figure out what HE should play, hope that helps with the thought process ^^