Define what you mean by safe.
1. Pregnancy risk.
If you're using birth control this will reduce pregnancy risk - you don't state what form of birth control you're using but I'm going to assume the combination pill which is 99.7% effective with perfect use. For the record it is biologically impossible for hormonal birth control to regulate periods (a regular withdrawal bleed on the pill is in no way the same as a regular period) - it's very important you know how your birth control method of choice works.
If you feel safe enough to rely on the combination pill alone then yes you can allow your partner to ejaculate inside you, but do know that the combination pill used along with withdrawal (pulling out before he ejaculates, and urinating after ejaculation so no risk of sperm in pre-ejaculate) that is then 99.98% effective with perfect use.
It's also important you know how to use emergency birth control if needed, although the combination pill protects you it may be that you don't realize util after you've had sex that you've forgotten a pill and in that case you'd need to know where to get emergency contraception like Plan B and how to take it to reduce pregnancy risk.
Birth Control Bingo: The Combination Pill -
http://www.scarleteen.com/birth_control_bingo_the_combination_pill
Emergency Contraception -
http://www.scarleteen.com/article/abuse_assault/emergency_contraception
2. STI/STD's and general infections.
Condoms and other barriers are always a good idea to stay safe, or at least reduce risk.
Remember even with regular STI/STD screening remember that there is no test for HPV in men, some STI/STD's take time to show in tests, some STI/STD's can be contracted by means other than sex, people cheat, and general infections such as yeast infections or urinary tract infections can be passed between partners via sex.
After Contraception or Commitment, Why You Still Gotta Rock Safer Sex -
http://www.scarleteen.com/blog/heather_corinna/2013/02/18/after_contraception_or_commitment_why_you_still_gotta_rock_safer_sex
It's all about risk assessment - understanding your risks and reducing those risks. You have to decide if you trust your method of birth control and your partner enough to go without condoms or withdrawal.