Do you really need a flowchart? There are decisions following decisions. You get yours as well. Plenty of them, in fact. You can decide to not have sex with a woman you do not trust. You can decide to ask her about contraception. You can decide to use contraception yourself if she does not. You can decide to use contraception yourself if she says she does but you do not trust her.
If you still have sex and forgo contraception, however, you are out of decisions. It's time for you to man up, grow a pair and face the consequences of your decisions.