Step 1 - Try to remove the emotion from the discussion.
Look at it from the other person's point of view before proceeding. They needed a ride, they talked to a friendly-looking coworker and he agreed to do it for 4€/day. OK, fair enough! So you ride with him, talk to him, tell him about your new raise and other personal information. You go to lunch together every day for months. You consider him a work friend.
But then apparently the other person nurses resentment in his heart, without telling you, and due to his envy over your 9% raise, freaks out and terminates the arrangement without notice.
Do you really want to be that guy? It'd be one thing if this person had done anything at all improper or rude, but he's not really responsible for the emotional issues you've developed on the side.
Also keep in mind how this looks in a professional environment. This can be interpreted as envy and spite, and that would concern others working with you at work. In every workplace "job roles" and whatnot are only 50% of the story, everyone either goes a little extra to help each other and collaborate and such or they don't. If someone else's team gets a little more budget, are you going to refuse to work on things they ask of you? You put those thoughts into their minds if you handle this carelessly.
Step 2 - Decide what you want.
Do you just want to stop this arrangement under any circumstances? Or do you want to renegotiate? If you want to renegotiate, what conditions are you willing to accept? If he was paying 4€/day previously, what do you think is fair now?
Proportionately, if he went from 28% higher salary to 39% higher salary, then math says it's 4.34€. But I suspect that's not really what you want.
I get it. I wouldn't give someone a ride every day for any amount of money, I'd find it too constraining on my schedule. But everyone's different. Do you just want to stop, period, whether he was offering 4 or 5 or 10 euro? Do you want it to be 4 days a week instead of 5? What, exactly do you want?
Consider what else you're getting out of this. A work friend and ally? Company on the drive? Heck, you could apparently learn from him how to negotiate a higher salary...
Step 3 - How to negotiate professionally.
If you want to negotiate the terms, you just say "Hey man! I've enjoyed our rides together, but I really didn't anticipate the impact on me. I can't come and go as I want, I'm going out to eat when I wouldn't sometimes... Is there any way we could change our agreement a little?" Then discuss whether more money, or only doing it 4x/week, or for only 3 more months, or whatever it is you want. Under no circumstances mention his salary, it would reflect poorly on you.
Make sure it is something you can live with, as going back to re-re-negotiate in a short period of time would come across as grasping.
Step 4 - How to bow out gracefully.
If you decide you just absolutely don't want to do it, or you can't come to an agreement on a change, you just say something similar. "Well, I've been happy to help you out for the last couple months, but I really want to start just driving by myself. Can we say next Friday will be our last drive together? No hard feelings. Let's keep meeting up for lunch!" or similar. Be open to doing it up to 2 weeks as a considerate gesture.
The friendliness and grace period means there will be very little chance of resentment or work fallout unless he's a colossal ass, and you say he's a nice guy.
You can come out of this as "the nice guy who helped me get to work for the first couple months and is now a work friend" and not "the unreliable jerk" to him (and others in the office) if you handle this with thoughtfulness. The Internet Tough Guys are happy to advise you to just tell the guy off and leave him on the side of the road, but I imagine you do care how you're perceived afterwards.