Men and butt stuff

I have been dating my boyfriend for about 7 months now and we have always been a pretty kinky and sexually comfortable couple. We like to try new things or get a little rough.... but around 6 months he got comfortable enough and started moving my hand towards his butthole while I was blowing him or if I were on top during sex... finally getting me to put a finger in there. It made me really really uncomfortable at first but I never told him because I could tell he was kind of uncomfortable too like he wanted me to do it but didn’t want to talk about it afterwards. But now we both have gotten more comfortable and he wants me to do it every time. My question is: is this normal for a man to ask me to do this? Should I be concerned that he wants anything in his ass? And as a guy, does it feel good? I just need help understanding it. Would love a guys opinion!