I don’t think Kirk is a womaniser but rather he’s the male version of the “femme fatale”. He treats his sexuality as one of many tools he used to defend his ship and accomplish his objectives. The main people (probably 95%) he directs his flirtations with are actually villains. People who capture him or put his crew at risk., He then uses his sexuality to get information, attempts to persuade them to stop being villains or allow him to escape etc to get his way. His flirtation is really less about him getting laid and is really an extension of ship and mission goes before everything else. He generally only flirts with people who threatens the safety of the ship
It’s just weird that Star Trek TOS has remarkably large amount of female villains in the show
He actually very professional to female colleague and only when he falls in love (ie Edith Keeler, the lady in the American Indian like planet and the Female Robot) does he acts on these. There been times when other female colleagues flirts with him and he generally rebuffs them if he does not reciprocate feelings.