I'd say it really depends on how he approached it with you.
I think it's unreasonable to expect that he would put his (obviously not ideal) relationship situation at a lower priority than your bachelor party. I mean, it's not your wedding, right? It's just a bachelor party.
On the other hand, if he's committed to planning this, then it's shitty to pull out.
In my opinion, there's a world of difference between "Yo dude! Got a better offer, so I'm not planning your Bachelor do anymore!" and "Yo dude, I'm really sorry, but I have this opportunity to actually spend some time with my girlfriend, and I don't know if I'm going to be able to plan the Bachelor Party".
Finally, it is NEVER selfish to feel upset about stuff. Feelings are feelings, yo. But perhaps it's helpful to talk with your friend about how you *feel*, rather than framing things in terms of how you (rightly) think he's dropping the ball on his obligations.
Something that you will almost certainly be confronted with at least a handful of times as the wedding gets closer, is the fact that nobody else gives, or can be expected to give, the same amount of fucks about your wedding as you do. There absolutely will be situations where stuff that is very important to you seems like "no big deal" to friends. And it's important to recognise that this doesn't make them arseholes, and it doesn't make your priorities selfish.
As always, communication is really important. I think that talking to your friend about how you feel is probably more constructive than asking a bunch of anonymous strangers on the internet whether your friend is being an arsehole or not.
(And I really don't mean that last sentence as passive-aggressively as it probably comes across).
TALK TO HIM!!!
