When you know that you are doing wrong then why you want to go for it and invite guilt for the future?! Your boy friend is remaining busy in newly started job can not be the reason for cheating him. Second gentle man seems to be flirt and fraud to me (devote ur mind for career, heart for love and body for enjoying!!). He has slept with many girls and provoking you for the same shows his character. He is seeing you as sexual object and surrendering to him is foolishness. You will surely regret this in future. Looking to his ideas about enjoyment, having multiple relations in past and always trying to excite you; you should never ever trust him to meet him alone. Stop talking to him, immediately break the relationship and never try to explain him that why you are doing this, if you want to come out of this.