Need Relationship Advice

Hi so I’m someone who likes to give some context prior to things so On Tuesday, my boyfriend responded at 5:30-6:01pm on his way back from work via train. Then I responded at 7pm to 8:13pm and then he responded 9:42pm So from 6:01-9:42pm he’s free boy and He’d take about 15-20mins to shower We hung out the night before and he didn’t tell me he had a dental appointment the next day. But he got a dental appt after work. He didn’t tell me with who. But he later (next day over call, mentioned the dentist was x girls name from our church) How he told me he had an appointment was he asked if I’d ever be a dental assistant as that thought ran past his mind during his dental appt. I said is this at Y person’s place (our guy friend dental place because he does hire people sometimes). He said could be his or anywhere else and that dental practises seem to look out for assistant. We called that night and he never once told me himself that he met up with X girls because she’s his dentist. Her dental work place closes at 7pm that day. If he’s the last person, I just wonder if they went for dinner together because he didn’t reply until 9:45pm. Usually before he replies, he’d shower first and that takes around 15-20mins. So he’d have to be home around 9:15-20pm ish. Means drive back around 9-9:05 latest ish. That still gives 7-9pm of him not replying to my messages. So I wonder if he was with her and didn’t tell me about it, even when I’ve asked for transparency Anyway, that night ended, we went to sleep etc. Next day, I went to the city to hang with friends and he was wfh. Before I got home, I entered my car and he responded. So we talked over the phone. Took me about 20-25 mins to drive back to mine and when I got back to mine it’s 11 ish and we played some games on our phone and he said he’s gonna sleep soon. He’s got his mouthguard in which he has not used in a while. I said oh you’ve not used this in a while. Then he said he for to a dental appt yesterday and was told he needs to wear it. Then he added that X Girl was his dentist and I was trying to react calmly I just said oh and he said his quote has ended so he’d need to come back next January to fix his teeth and she pleaded for him to wear mouthguard in the meantime to protect it What does this mean? Why didn’t he just tell me before and how long do you think he’s with her? Also context, sometime in September, a week before My boyfriend asked me to be his official girlfriend, X Girl messaged him and asked if he’s free to go for a walk. He was with me the whole day and didn’t see it so few hours later he responded saying no did you end up going for your walk? He later told me about it and showed me the chat. He was confused why she asked him for a walk as they’re not as close. I appreciated that transparency then. However, I can’t get this past me. She’s also my friend and we were close. But I feel like we’ve not been as close. Not sure if she’s holding back or if I’m holding back but it’s a little awkward between us though we still hug and say hi and talk and yeah. But the next day, we had an event and she was there with our other friends. In front of them, my boyfriend said I was over for dinner at his place. I thought that was nice But yeah the recent event made me a little insecure and why he didn’t tell me he was meeting her? Is it because it’s just an innocent dental appointment so he felt no need to ? Or because there’s something more? I’m also quite new, and learning. Learning how to regulate my emotions in this relationship and would appreciate honest but kind advice ! Thanks