Thomas is still able to feed -- see Lara feeding him energy in the boat at the end.
It's just that Thomas was beaten until his Hunger stopped healing the damage, because it was out of energy. It's like what the Naagloshi did to Thomas in Turn Coat, but without the delicate balance.
If Thomas had that love protection thing going from being with Justine he wouldn't have been able to feed and Lara would have been burned from just touching Thomas. So we must draw the conclusion that either Jim made a mistake in letting Thomas feed energy from Lara, and I don't think Jim would make that obvious a mistake, or there is another explanation. (If nothing else, several of Jim's BETA readers would have caught that error and pointed it out.)
The other and more natural explanation is Thomas did go to feed his hunger, just as Harry recommended. And where could Thomas go to feed in manner that would not cause harm to his partner? To one of the ladies in the swarthalf court, most likely Evanna. We haven't really met any other swarthalf ladies, so Evanna makes the most sense.
This would mean that Evanna lied to Harry and she's wrapped up in the conspiracy to kill Etri, probably I'm not sure this entirely rules out Ebenezer's possible involvement. Theoretically, with the use of the Blackstaff, Ebenezer could have put a mind whammy on both Thomas and Evanna. What was the necessity for Eb to break through the Swarthalf defenses when he went to visit Harry? Was Ebenezer really that annoyed by having to follow their protocols? I didn't believe Eb would have to wait days to see Harry. Eb could have sent a message to see Harry and met him a neutral location like Mac's. So perhaps breaking the Swarthalf defenses allowed Ebenezer to get a close look at what he would be up against in order to more covertly penetrate their inner sanctums. It's a bit of a stretch, but not an impossible one.
That's an interesting thought. Add to that -- Lara's great victory was getting Thomas moved to Marcone's stronghold, where it turned out there was a glaring opening in his defenses. If this was his plot, you know he's got lots of video of Lara and Dresden breaking Thomas out.
I'm not sure how he'd provide what Thomas needs, though. He might be able to buy help with that from Odin, but why wouldn't Thomas be able to just buy that himself?
Aren't we missing something here? Lara gets Harry's temporary service in which he must fulfill two favors for her. When Nicodemus got Mab to loan him Harry, Nic had specific uses in mind for Harry; opening a way to Hades vault and getting through the Gate of Ice. Lara never gave a hint that she needed Harry for any specific purpose. Using Harry to get an introduction to Cristos seemed to me like a really minor use of one of her favors, but even if it was necessary it should have come at the expense of something else. Using Harry to rescue Thomas was a necessity, but it still should have futzed up her original plans, assuming she had any. Yet Lara never complained or even mentioned that some scheme she was working on had been derailed by Thomas' actions. It's like Lara knew she would need Harry to rescue Thomas.
I hate to say this, but it's kinda weak writing. If Lara set this up, even Harry should quickly be able to see through something so transparent. If Lara didn't set up this situation, it's still not good because she should have been annoyed that Thomas upset her original plans.