Lol!!! I'm surprised nobody else got the Eminem "8 Mile" reference!

I'm going to assume you're running at least 5 days a week, if not you should be-6 would be better. vary your distances-2 miles then 5 miles then 3 miles then 6 miles then 2 miles then your long run, then a day off-just some walking. Don't jump from 8 to 9 miles, do 8.5 miles for a while, get used to the distance for a while, then move up a little at a time. And go a little slower for the long run, your energy will last longer. The miles during the week will build your base, which from the sounds of it you need. Do your carb load the night before, doing it the day of is useless, just some fruit or light carbs about 5-6 hours before long run, you want an empty stomach. And keep hydrated, and stretch a lot. BTW-when I was your age I was doing 70-90 miles a week, so if you have any questions please ask, I'll be glad to help.

Not bad

Keep going but don't push yourself too hard! Try drinking more water and possibly try a different kind of carb to use for your carb load. Also it's easy to take in too many carbs that will weigh you down on your run. You really don't need a huge meal for a longer run. I keep my dishes to 2 servings of pasta max plus maybe a slice of bread for tomato sauce. Trying practicing variations of kinds of food and the amounts of food in conjunction with shorter runs so that you can feel out how your body reacts. After the 10 mile mark your body gets dehydrated and plan your run along stops where you can have a small intake of water to keep you going.

Here is the physiological reason you vomit while running.

When we exercise our blood leaves the stomach to move into the muscles needed to perform tasks. The more intense the exercise the more is required.

For you, at mile 8 to 9 (based on your intensity) is when your digestive tract is completely depleted of blood and shuts down. Instead of the normal function keeping the system flowing, you have a sack of material bouncing out of you. Imagine jumping while holding a glass of water. You couldn't do it without the water spilling out.
This is why you notice it on your shirt, as opposed to having all the normal contractions that go with vomiting.

You can try slowing yourself down, taking a little longer to complete your run. During this time you can fuel up with easily absorbed carb gels, while also drink water. You need water or the gels on their own can make it worse.

Here's a better solution. The less energy your muscles use while running, the less likely this is to happen. If you're not already, add some resistance training (weight training) to build strength in your legs(although whole body would be better).
The more muscle you have to power each step during your run, the less you'll be depleted. This is a game changer.

Don't go crazy at first and make sure you're using the proper form. I suggest lunges over squats (definitely). Lunges mimic the running motion more closely and you are less likely to injure yourself. Also, lunges will strengthen each leg equally, where your dominant (stronger) leg may continue to build greater strength during a squat.

Either way, make sure you're doing them properly. In my opinion, lunges are better.

I apologize for the detail, but you didn't mention whether you lift already and I believe the details are important.

It might also be worth understanding why you need to complete additional miles. 8 mile completion is evidence of a very fit cardiovascular system. If more is just to prove to yourself you can, you will be proving it to your detriment. Vomiting is a sign your body is in a state of struggle, and should happen a few times in a lifetime, not several times a week.

Good luck!

Have a United States Marine D.I. hang out around the beginning of mile 8 to shriek motivation at you for miles 8 and 9! You'll make it easy! I repeat EASY!

I was always amazed at how much I could do with a screaming staff sergeant or gunnery sergeant screaming behind me when I was in AOCS! (Aviation Officer Candidate School, like the movie An Officer And A Gentleman)

Sounds like you are admirably pushing yourself to a goal! I like working towards goals...how soon after you eat are you running? I can't eat hours before any strenuous workout...maybe if you ate your carbs at dinner the night before it would help. I also find tomato based things seem to upset my stomach...a friend told me to drink a glass of bicarbonate soda to cut the acid and it seems to help. Drink plenty of water ahead, too...if you get thirsty, it is too late...good luck...listen to your body, but keep on pushing the limits...you will see your goal met with your determination to overcome any physical obstacles.

What is the point of nine versus eight? If it's just a number, perhaps you should re-think whether it's worth it. Your body is telling you something.

If the nine miles is part of a broader fitness goal, consider another way to get there. I can't run well but can hop on a Concept2 rower and bang out a half marathon just about any time. FInd what works for you. Running too far doesn't seem to be it.

One other item: I never carb load, since I eat few carbs.

Lose yourself in the moment