1. Any time you have sex there's a possibility of pregnancy. The pull out method is not a form of birth control, so don't use it (unless you pair it with something like condoms) and don't worry about it.

2. Again, nothing is perfect (except for abstinence of course), but condoms are very safe.

3. No, in general sperm can't get through clothes. He’d have to ejaculate directly over your vagina on your underwear for there to be any chance worth even considering-- but that's still pretty small chance.

Here are some tips to avoid your worries:

If your vagina is going to come in contact with your partner's penis, ejaculate, or if your partner is possibly going to ejaculate on your underwear, then use a condom. Whenever you're in doubt, just protect yourself against whatever bizarre situation you can imagine. It's a lot less stressful that way-- not to mention less messy.

If you are having sex and are not comfortable with the failure rate of condoms, you can continue to decrease chance of failure by adding on forms of birth control-- like using condoms with spermacides or using hormonal birth controls, condoms, and spermicides. It just depends on what chances of pregnancy you're comfortable with.