Background
I have been living with my boyfriend for three months. Both of us are working as trainees in different companies, but while he has 2 hours of daily commuting, I can reach my workplace within 15 minutes with my bike. Regarding this disparity, we decided that until we go back to school (i.e. in two weeks), then I would do the cooking. I totally agreed on this because I come home 1 hour earlier than him plus I love cooking, while it's just another chore for him (he wouldn't mind doing it though, it's just that he's not interested in it). For the other chores, we shared them in a more or less fair way (we did almost all chores at weekends, so I'd say I was doing 60% of the chores).
Situation
A week ago, his sports training began (2 hours three times per week, so one thing leading to another, he gets home 2h30 later than before). He has no choice in the date and time of his training, but I do for mine (I train at the gym 4 times per week, 1h30 each workout), so I adjusted my trainings to match his, but I still come home an hour earlier than him. Naturally, I persisted in cooking our meals. The problem is that since he gets home later, he does less household chores than before. For example, now I am always the one sweeping the floors, cleaning the windows, ... while we used to share these tasks before.
Last weekend, he said he noticed than I cleaned the whole flat while he was on a holiday with his family (I also had a party this weekend with my friends who moved to another city. I woke up earlier on Sunday before joining my friends to do the housework so as when he gets back after so many hours on the road, he finds a clean place). He thanked me, and said he was sorry that he didn't do that much for housework the week before. I said it was ok, but we're now in the middle of the week and he's still doing few chores. Yesterday I did the housework and gave him 3 fast and simple things to do for when he comes home, but he takes so much longer than me to do them so I wanted to help and he got mad. In the end I stopped helping him and he did not do one important task I asked him, though I know that if I had done it, he would have remembered and maybe again told me that it was his job. I feel guilty about this.
About us
He has never refused to do any chores, in fact he's willing us to fairly share the load. He never takes any initiative though. On the other hand, I'm the "if there's a chore to do which is not part of my job but I have the time to do it, I will take care of it" kind of person. Not really because I don't like living in a dirty place, more because I don't want to bother others. Just for the record, this is not a relationship problem, I used to act the same with my former flatmate.
When we moved in together, I suggested that we make a schedule for the chores: who does what and when, but the idea fell by the wayside. To add further details, we earn the same wage (to be precise, he earns 20% more than me but I have equivalent benefits in kind) but we do not have a joint account. We pay 50% of the groceries each.
What I want
For now, I don't mind doing almost all the housework (90%). What I am afraid of is that it becomes a habit that I handle all on my own, and I do not want this, because I'm afraid I'll get exhausted and we'll fall into a huge fight - he never refused to help after all! I think that sharing the load more fairly is the only way to avoid this problem.
How can I politely tell him we need to organize for doing the housework?
We're a couple from Western Europe, both in our 20s.
Update
Thank you all for all these valuable answers, it helps a lot. I had a chat with him yesterday, explaining the situation (he comes home late, I'm currently doing most chores and don't mind but wouldn't like this to become a habit, and so on). He totally understood. We agreed on creating a schedule and assigning ourselves to each chore, regarding our willingness to do it (for example I don't like wiping crockery and he doesn't like cleaning the composter) and the time we spend at home. We also agreed on a frequency for each chore (e.g. sweeping the floors twice a week) and that if the time planned does not suit our actual timetable, we can postpone it. It's not very precise but knowing my boyfriend, I know we can make this work. So I'll still do more than him in terms of quantity, difficulty and duration but it's fairer and it's something we agreed on so it's totally okay. More, based on threetimes' piece of advice, we'll review the scheduling anytime our timetables significantly change (i.e. in our situation when we go back to school, by the end of the month).
Thanks again y'all.