Hi there, thanks for your question. It sounds like you are a bit concerned about your girlfriend asking you to cum inside her.

You should never feel forced to do anything sexual that you feel uncomfortable with. If the idea of cuming inside of your girlfriend doesn't feel right to you, then it is probably best not to.

Maybe find out the reason why your girlfriend asked you to do this. If you have been in a relationship for a while you should be able to talk openly and honestly with each other, and it can be especially important to talk about your sexual relationship.

Girls often take longer to reach orgasm than guys. Foreplay can be particularly important in bringing a girl to orgasm. Because you are pulling out to cum, you may not be pleasuring your girlfriend. This may be one of the reasons she has asked you to cum inside of her, so that the sexual act lasts longer and she may have a better chance of orgasming herself.

You say your girlfriend is on birth control. If this is being taken correctly, the risk of pregnancy would be low. Another reason she may want you to come inside of her is to make her pregnant. This sounds unlikely based on what you have said, but it might be a good idea to check with her. Having an open conversation  will help to work out some of these possibilities.

Ejaculating inside a partner is a normal act of sexual intercourse (vaginal sex), but in terms of safety, you need to consider possible pregnancy and also the risk of sexually transmissible infections. If you or your girlfriend are having unprotected sex (especially with multiple partners or have had several sexual partners in the past) a regular sexual health check up with a doctor or nurse is a good idea. This is to make sure you are both sexually healthy and don't have any infections.

Have a look at the link below to find more info on safer sex, female orgasms, etc. All the best.