f4m I regularly perform oral sex for my best friend, and we never talk about it

I (f24) have known my best friend (M25) for three years. We became quite close right away after meeting and spent a lot of time together, but nothing romantic or sexual happened at first.

We were hanging out at his apartment a few months back, watching movies on the sofa as we always do we'd both had a couple of beers but nothing too insane. We were under a blanket and rather close to each other due to the cold, but this was not unusual. After a bit, I was leaning on him and my hand dropped close to his lap, and I realized he was semi-hard (he was wearing loose pyjamas and no underwear, so it was rather visible). He froze a little as I accidentally brushed it, and then I'm not sure what happened, but I touched it properly, and he moaned. I began stroking him off, and after a few minutes, I placed my head beneath the blanket and began using my lips till he entered my throat. We didn't say anything or make eye contact throughout the entire experience. We didn't acknowledge it right away and went back to normal. However, when I met him again a few days later, we were sitting normally when he pushed my hand to his crotch. I took the hint and ended myself on my knees in front of him on the sofa till he came. This now happens practically every time we are alone, and he has grown bolder about it, holding me by the back of my head and using my throat as a fleshlight until he cums. Sometimes he sits with a beer or cigarette in one hand and moves my head with the other. He sometimes holds his phone and watches porn as I blow him. This has only ever happened in either his or my house, except for one occasion when we were both at a party and were left alone in a spare room; this time, he grabbed my hair suddenly and pushed me onto my knees before undoing his pants and dragging my mouth onto his dick and fucking my face until he came, then we returned to the main room of the party without saying anything and resumed socialising and chatting as usual. We never discussed it, and we never looked at each other while doing anything. He has never sought to reciprocate, nor has he attempted to take things further by having intercourse with me. At this point, he is essentially using my throat as a toy to jerk off with. And I love it. None of our friends know we behave absolutely normal with each other until when this happens we simply ignore it and pretend it does not happen every time we are alone.