My boyfriend doesn’t get that hard/stay hard. Explanations?

Alright so.... Me and a guy I’ve been dating made things official about a month ago. This is the greatest guy I’ve ever been with; everything has come so naturally, we are both secure and comfortable with one another, we just seem to match up perfectly in every way possible and we are both so incredibly happy. BUT, I’ve noticed some things about our sex that I haven’t experienced with anyone else and I’m a little confused, and I’m wondering if I should be concerned. The first time we had sex, I noticed that he was slightly less hard than any other guy I’ve been with. But he finished almost instantly. It was like that about first 5 times we had sex. I didn’t find this part unusual. As time passed, he started to last longer but I began to notice major inconsistency in his hardness. I know he’s attracted to me, he tells me all the time how attractive he finds me. And he seems to have a very high sex drive. He usually gets aroused just from us making out and we usually end up having sex every time we’re together. Things go one of two ways: he gets moderately hard and finishes quickly. Or he has trouble staying hard and it takes very fast paced, rough sex to do the trick. I would say it’s about 50/50. Sometimes we have sex multiple times a day, and it amazes me how he’s able to keep getting aroused or get hard at all and finish, but he does. He seems to stay harder in certain positions than in others, but he says he has no preference other than liking to “change things up” and not stay in the same position for too long. This is the extent of our conversation about it. I’m scared to actually bring it up because I don’t want to make him feel insecure, and I’m also worried that maybe he’s attracted to me, but his body isn’t as attracted to me? I’m not sure. But it’s like sometimes he goes almost completely flaccid mid sex despite seeming to be completely into it. The sex still feels good, as long as he isn’t completely soft. But I haven’t been able to finish yet because when he is hard enough and it feels the best, he doesn’t last, or when it lasts longer I’m sitting there wondering why he isn’t that hard for me and it doesn’t feel quite AS good. This guy is completely healthy, he works out, his diet is great, he seems to have a healthy level of testosterone and has a high sex drive. He doesn’t have any mental illnesses or anxiety. Doesn’t do drugs or drink much. The only thing I’m unaware of is if he watches porn. We haven’t talked about that yet, but I know excessive porn consumption can affect this. But I don’t get the impression that’s the issue. We are together every once of free time from work he has, so I have no idea when he would even have time to watch it. At this point I’m not worried about me getting to finish, sex is the last of my priorities with him. But I want to figure out what’s going on and work on it WITH him eventually. I just don’t know how to talk about it. So I’m curious what anyone else thinks about it, what the cause could be, if anyone else has experienced this and what they did to help.