womaniser — Non-Oxford British standard spelling of womanizer.
casanova — Giovanni Jacopo (dʒoˈvanni ˈjaːkopo). 1725–98, Italian adventurer noted for his Mémoires, a vivid account of his sexual adventures and of contemporary society
don juan — a legendary Spanish nobleman famous for his many seductions and dissolute life.
lothario — (sometimes lowercase) a man who obsessively seduces and deceives women.
philanderer — (of a man) to make love with a woman one cannot or will not marry; carry on flirtations.
playboy — a man who pursues a life of pleasure without responsibility or attachments, especially one who is of comfortable means.
seducer — to lead astray, as from duty, rectitude, or the like; corrupt.