any way to avoid being so tired after longer runs?

Sleep more if you can, not always an option if you have a job or kids.

What's your hydration like? Most people drink well before they set out for a run and when they get back, but really you need to be hydrating properly for 48 hours before a long run.

You could also take a gel just to add a few calories while you're on the run.

Reduce your sugar and simple carb intake a lot. Its challenging at first. But your energy level will even out so much more. And you'll feel the difference whenever you have sugar. It isn't worth it.

Also get off screens as much as possible and work on your sleep schedule.

Eat way more fruits and vegetables

Surprised this hasn’t been mentioned but your long run is probably disproportionate to the rest of your week. Focus on running every day and adjust your paces. Your body will better tolerate a long run when it better adapts to cumulative fatigue.

Drink 1 - 1,5 g per kg bodyweight of carbohydrate and about 0,5 g/kg bodyweight of protein SOON after you finish your runs (ideally within 30 minutes). Activity of the enzymes which restore youre muscle glykogen is way higher shortly after the activity and your body uses less plasma proteins as amino acid source for repairing your muscles.

My standard recovery drink after hard/long workouts is: 1 banana with 1 big spoon of maltodextrine, 1 big spoon of whey protein, a little bit of salt, mixed with low fat milk. Since I'm doing this I feel like I'm recovering way faster from hard workouts. Of course eat more normal foods over the next hours (without overdoing it).

When marathon training, I've generally done my long runs (up to 22 miles in 60-65 mile weeks) on Friday morning before work. My work is desk based so not physically demanding but I could still work effectively and didn't have trouble concentrating. If I do a long run on the weekend I tend to laze around afterwards. It's like I can override the tiredness by being in work mode.