Yes. This is normal. My intact male turns into an idiot when the neighbors' dog is in heat. I don't know if there's a point where you should worry about him mentally, but he will do whatever to get after her, so a ripped up kennel and an injured dog is a possibility. As for eating, I "spice up" his normal food with some gravy, raw meat, or wet food and he'll eat a bit more.
I applaud you for being responsible and keeping them apart. Are you planning on breeding them or are you doing a late spay/neuter? Not judging, just curious.