Using the calendar method is a very bad idea because it limits the number of days on which you can have sex (and why going for that??? What is the reason?), is unreliable, error-prone, and labor-intensive in terms of upkeep. And, no protection against disease. Basically, nothing going for it except for total lack of side effects but then again, it is labor intensive and. Requires a lot of dedication.

So no point.

If you really cannot talk to him about it, at least get on the Pill in the meantime.