The way I see it, contraceptive is for the person using it. So if the guy doesn't want the girl to get pregnant, or wants to avoid STIs - he should use the app

The way I see it, contraceptive is for the person using it. So if the guy doesn't want the girl to get pregnant, or wants to avoid STIs - he should use the appropriate protection. If the girl doesn't want to get pregnant, or wants to avoid STIs - she should use the appropriate protection. (Both people want to avoid pregnancy/disease? Then both should use protection!) That way you don't need to worry about what the other person is doing - you manage your own expectations. If you're in a stable long-term relationship and have talked about it, then sure, you can rely on one person, but otherwise each person should, imho, manage their own contraceptives.