You are in a monogamous relationship if you and your boyfriend don’t have other sex-partners. If both of you have been tested for HIV and STIs and all the results are negative, you can choose to have sex without a condom. This also applies to those who are undetectable and STI free.
It is a possibility that your monogamous relationship can change over time. So always discuss your current situation.
We recommend you both to get tested for HIV and STIs at your doctor, the STI clinic of the GGD or at Man tot Man Testlab. Find more information about it here.