I don’t know how can one believe that a person is serious about building a seriогs relationship if he is treating himself so unseriously that is not able to write without mistakes.

I’ll comment on two objections in advance.
1. Many men of genius were illiterate.
Comment. Are you genius?
2. There are people who are medically unable to learn to write without mistakes.
Comment. Are you the one? Do you have a medical certificate?
3. Illiteracy does not mean lack of serious attitude towards oneself.
Comment. Yes, it does.