Relationship problem need advise

Been in a 15 year relationship and what I’m asking is for you advise. My boyfriend has this female friend that I’m not to fawn about. I have felt like he has this thing for her for example, she has always cut his hair but when got together I told him that it didn’t look right him going to her apartment by himself. This female is single and every time he went he would take almost 2 hours. He saw nothing wrong with this at first and we had a big fight . Finally he understood so she would come over instead and cut his hair. I was fine with that. Then one day while I was at work our roommate and his female and the other female invited him to go out and he went. I didn’t find out till the roommate told me. This really upset me and it’s cause of this I begin to really dislike my boyfriends female friend. Now about a year ago they became friends on Facebook I didn’t say anything I let it it ride but than just recently I saw how many times he was liking everything she would post and comments which was at least 10 to 15 times a month than on his birthday she posted twice and on one of them she puts happy birthday handsome. I brought this up and told him this is not right he has disagreed with me and claims that I looking at all wrong and that he dose not have a thing for her yet he will not remove her from his Facebook page. So I’m asking am I not need to worry about this and let it go.

Thank you for your advise just as i suspected.