How can I make sure I don't ejaculate so quick?

Lots of choices. Are you male or female? Lots of causes including stress, depression, low testosterone, premature ejaculation and many other causes. Have your partner ask for help first from the family doc and possibly a sex therapist. This problem can usually be fixed. If you are his female partner, then think of it as a compliment, he is so excited by you he his orgasm happens quickly. Topical numbing cream help.