Answer: If you suspect an STD, it is important to see a doctor as there are some STDs that can get worse over time.
Explanation: There are several STDs, where many are not symptomatic and come to manifest symptoms after a long time. In the case of women, STDs that are not treated can cause other infections and even problems in the future to have children. In the case of men, they can also develop infections.
If I have a friend who needs my support, what I can do is accompany him to the doctor to seek treatment and remind him of the importance of protecting himself when having sex.