We’re human and we’re sexual beings and it’s all normal. The fact that you’re pretty sure he’ll be ok with it on at least a basic level is a good sign and I bet you’re right. As far as I’m concerned, lots of topics are awkward and difficult in therapy and this is no different. Is there a way you could ease into it, maybe by saying you have a topic that’s difficult to bring up and that you’re not sure how he’ll respond? Or could you send an email in advance so that you know he won’t be surprised. Or even print out this post or a version of it and give it to him to read?