I need help

My son was born in March of this year and I was dating this guy for 2 years and we tried for a baby...

He left to new york and we broke up so in the same week frame I met a guy and slept with him... and was pregnant....

Now my ex who left to NY is convinced it's his son... I cant tell and dont wanna waste money for a DNA test so can I can some thoughts..... cause I really dont think so.. but he is convinced and so is his family... I just want to see if anyone can give me some thoughts cause I cant tell cause he looks like me

My little man

My ex

Sperm donor