You can make warlocks decent in melee, but not Wyll. Wyll just doesn't have the stats for it - with 9 STR and 13 DEX he's just going to be bad at using weapons no matter how you cut it.
If you want a custom melee warlock, what I would do personally is play as a half-elf (any type would be okay I guess but half-wood elf is probably the best because of the increased movement speed) and get 16 DEX, CON, CHA - the leftover 2 points don't matter a huge amount, probably put it in WIS for the saving throw. Since resting is freely available in this game, you can use armor of agathys + hellish rebuke (or any 'lasts until long rest' spell), then short rest to recover your spell slots and you'll still have the buffs up after a short rest and still have all your spell slots available in a fight. You can dual wield daggers, and either cast a spell + attack with offhand or just attack twice (and be sure to try to get backstabs of course for the free advantage). Hellish rebuke is a decent way to use your spell slots with this kind of build, but you should be warned that it's very buggy and often doesn't work properly, especially against enemies that can push you or knock you prone or enemies that have multiple attacks per round.. but when it does work it's pretty decent.
As far as higher levels go, I wouldn't count on it. Warlocks don't get any extra attacks per round from leveling up, so the gap between them and an actual martial class at using weapons will only get bigger at higher levels.
