The birthmark thing is weak the make up videos on SM can make a 60 year old look 30 birthmarks would be no problem! He is certain so all you can do is accept his position. The problems you have stem from either secrecy or a lack of honesty and this is how it has manifested. All the excuses sound like just that to him. Why waste your time try to prove a negative, if it is not you, you dodged a bullet! If it is you he dodged a bullet.