<human>: Can you provide a brief rundown of the text in within 3 sentences?

My long term boyfriend has a large group of male friends from school ( so friends for about 20 years now!!), this group includes one female (who he has never been romantically involved with except a kiss in spin the bottle aged 14). I know that they are just friends and I have never been given any logical reason to be suspicious but I can not help this horrible jealous feeling I get whenever I see him and this female friend together. They are very close and there is understandably a lot of affection and banter between them, like there is between the whole group, but for some reason when it is directed towards another female it drives me crazy! I trust my boyfriend completely and am incredibly happy/ secure in our relationship other than this one issue. Logical, rational me knows I have nothing to worry about but this doesn't seem to help in the situation. Sometimes when we are all out together (usually involving alcohol) I have to go to the toilet and speak to myself in my head/ calm myself down and tell myself I'm being a total idiot. I also have a male friend who I am very close to and we do spark off each other, I view my relationship with him to be like brother/sister. This is exactly how my boyfriend says he feels about this friend so I should technically understand but it doesn't make it any easier! On top of all of this the female friend is in a very long term relationship herself.  We get on well with each other, and she says that my boyfriend has completely changed since being with me and that she loves seeing him so happy etc. I really, honestly have no reason to worry but I cannot seem to get over this insane jealousy issue. Any advice is massively appreciated!
<bot>: Looking for advice on how to overcome jealousy of partners relationship with female friend when I know rationally I have nothing to worry about.