I first realized my interest when I saw a photo of a woman in a Playboy magazine who was squatting and whose anus was clearly visible. I was so so turned on by the sight. But I felt ashamed for this interest. Later when I was 16, I had a girlfriend (15) and we started to become sexually active. One night, the first time I pulled off her panties, she was lying on her stomach and I began massaging her bottom and couldn't help but spread her cheeks just so I could see for myself. The sight of her anus (I still remember like it was yesterday: tiny, pale pink, no hair, barely wrinkled) was overpowering. She never let me insert a finger and she had no interest in my anus. However she did let me tongue her there as much and as often as I wanted.
It wasn't until college when I had a serious girlfriend who agreed to finger my anus. Finally -- what an incredible feeling it was. She said it felt "weird" (she had never done that before) but was happy to do it whenever I wanted. I still felt ashamed about this desire, but of course it was only something between me and her, and since she was OK with it, I was. She enjoyed when I would stimulate her anus (tongue or finger caress), but did not want any penetration, claiming it too painful. Once I asked to insert my finger in her bottom, just to see if she could handle it. She agreed and knelt, bottom up, head down. As I applied vaseline around her hole, she said, "See, I like that, when you touch around the outside". But once I pushed in (and I pushed in as deeply as I could), she said "No, that hurts" and wouldn't let me stay inside her. She didn't make me feel bad about it or try to make me feel 'perverted'; she just claimed that she was "too small there".
I've had several partners (all women) since college and am now married. All of those women (except one) enjoyed having her anus stimulated in some way (from caressing to fucking to shove-that-dildo-in-my-asshole) and all (except that same one) were happy to stimulate mine (again, some just caressing, some fingering, and one who strapped it on and fucked me). Of those women, 4 of them actually initiated the anal play: one simply told me one night, "I want you to fuck my ass"; one woman started loudly moaning "yes yes yes" the first time I spread her cheeks for a peek inside; one guided me to her anus as I was fucking her from behind while she lay on her stomach; and the other woman, while I was performing cunnilingus, simply turned over onto her stomach and presented her bottom to me, and I wasn't sure if she didn't like what I was doing to her pussy or if she now wanted me to do the same to her anus -- turned out to be the latter.
That one woman, the exception, was completely different and DID make me feel ashamed, horrible, perverted, and less-than-human. She certainly had her issues, and it became clear later that we were incompatible in many ways, and then broke up. Basically, the one time I dared to lick her anus (during a massage), she freaked out, accusing me of all kinds of things, including of wanting to eat her shit (no, I don't have that desire). Once, when I asked her why she was so against my stimulating her bottom, she said, "I'm afraid I might like it." Anyway, that was the beginning of the end for us.
My wife is very open to my desires, as I am to hers. It's clear that she doesn't have the anal-focus that I do, but she is willing to indulge me and absolutely doesn't make me feel weird about my desires (the first time she penetrated me with her finger, she later said it was a "strange" experience but that she was completely turned on by how it made me moan and groan). The first time I explored and kissed her anus, she was silent because she was taken by surprise and a little embarrassed but later said she liked it because it tickled. I have told her that I still have a sense of shame about my anal desires, that somehow I am perverted, but she has only been understanding about it, thankfully.