JackOfAllTirades
Explorer
Also, it would seem very apropos for a Pact Blade Warlock (of any Patron) to take a few levels in a martial class.
This can't make your patron too happy.
Is there any RP reason would continue granting powers to a servant who chooses to advance in other classes?
As a reason to multiclass, "concern about whether the DM will arbitrarily yank my class features because he has some weird idea that I'm betraying my patron by practicing with a sword" does not strike me as a good one.That's one good reason to multiclass out before level 3. Invocations are knowledge according to the PHB, and knowledge logically cannot be revoked, but a Pact Boon is granted in return for service, so in theory you could lose it.