We tried to have sex but his penis doesn’t go in. How come?

First explore your vagina. Take a mirror and try to find your vaginal opening. If you draw the lips apart you can see the entrance in between the clitoris and the anus. If you tighten and relax the PC-muscles you can see the opening tighten. Relax the muscles, wet your index finger with saliva and let it enter your vagina. If it goes in easily, enter with two fingers. If you involuntarily tighten the PC-muscles you have to learn how to relax them. Use enough saliva or a lubricant (water based). If this goes well, let your boyfriend do the same during lovemaking, when you are excited and your vagina is wet. If he can penetrate you with his fingers without any problem, try intercourse again. Take his penis in your hand and keep the tip in front of your vaginal opening, then let him push forward so his penis will slip in.

It’s also possible that it doesn’t work because your boyfriend is afraid of pain, for instance because his foreskin is too tight, his glans is oversensitive or his frenulum is too short. If that’s the case he has to solve that problem first.

See also: vaginismus, imperforate hymen