Anal sex does not need to be painful if you prepare yourself properly for the act. I have written on this subject on several occasions, so it would be a good idea for you to do a search for painless anal sex in our archives. You will find that I have written quite comprehensively about ways of preparing yourself so that anal sex is not only painless, but intensely enjoyable for both of you.
Ultimately, painless anal sex comes down to being properly relaxed, and well lubricated. It is not true to say that the anus does not lubricate, it does; but not to the extent necessary for you to enjoy anal sex without some additional lubrication, provided by something like olive oil, coconut oil, ghee, or KY jelly, which is available at most chemists. Saliva can be sufficient, once you are well practised in the arts of anal sex, but it is insufficient for beginners!!!
You might find that all of the preparation that I have suggested can be done by both of you following the guidelines. While he may not be able to start having anal sex with you immediately, he will definitely enjoy all of the steps of preparation, and you can continue doing these things as part of your erotic foreplay, whenever the two of you feel like it.
Once you are a regular practitioner of anal sex, you will find that it is easy to accept your partner's penis, fingers, tongue, or whatever else you may wish to feel pushed inside you, but to begin with, follow my guidelines, and you will lose any fear or apprehension you may have about this act being painful for you. Anal sex in all its different variations is something that I absolutely adore, and it is a most wonderful part of my regular sex life.
Kegel exercises are also useful, as a strengthen the pelvic floor muscles, and also give you far better control over both your inner vaginal muscles, and muscles of your anal sphincter, so don't underestimate the value of doing these exercises on a daily basis. You will find plenty of information on what these exercises entail if you do a search on the Internet.
Now, I suggest that you start searching through our archives, and you will find both my own advice, and that of other people who are also participants in anal games of all kinds. Once you have had a good read, you will be able to start preparations for something that you will enjoy just as much as he will!!!