I think you should bin the boyfriend , and give yourself a few months being single.
The fact is your self esteem has been rotted away to nothing by this louse of a man , with his repeated cheating . That made you vunerable to attention fron another man . Of course you had sex with the first man who paid you any kind of attention , i dont blame you or judge you for that at all , it was an escape from all the shit your boyfriend has put you through .
Its nice to be be wanted and desired . Its nice to feel sexy and lusted after .
But its nicer to be properly loved , and to have that , you first need to love yourself , and have some self respect and belief that your worth more and deserve better than a man who repeadly cheats on you , or a man whos willing to sleep with you knowing that you have a partner. .
Get rid of the boyfriend , tell the om to get lost . Give yourself time to heal over this and work out what you want in a partner . Unless your in a good place with your self confidence , you have no business being in a relationship at all . Without it you`d be vunerable to another waste of space man , and would get carried away with being " in -love" without actually looking at the character of the man in question.
Do not go near a bloke if he does not have a decent set of morals , regardless of how handsome or how rich he is .
Why dont you do something for you instead ? . Learn a new skill , or go for that fabulous job you always wanted ? .