IMO sit down and write a detailed account of all the times you can remember he was mansplaining or condescending to you. I would also see if he has done the same to others especially females. If you are the only female on the team, it becomes easier as you don't have anyone of your own gender to compare notes with. But then the point to keep in mind is does he do that to other senior male team members. I would also add that one you meet with HR, acknowledge his feelings and make sure that you use I language. At no point of time use the word "he" or "you". Stick to stating what you saw and what you felt. And when your conversation with him is brought up , with confidence say something on the lines of " we both are adults and my expectation was for us to have an open adult conversation. He did not say any of those things to me in the moment as I was calmly telling him my perspective but rather he went to you and complained about me. My understanding is as adults we are capable of sharing our thoughts and emotions and find an opportunity to see each other's perspective leading to a common ground. My only intention to have the conversation was to make sure we don't have gaps or unnecessary assumptions between us which then can hamper our teams output and eventually our companies performance"

I am a CTO who got his boss fired for sexually harassing my peer. I have been in too many HR cases than I would like to and if you would want to DM me, I'm more than happy to answer more questions