Tried to be friends with my ex - then found out that he cheated?

If I were you I would get out of the relationship for good.He is not trustworthy.It could be he likes you, but he has a problem with truthfulness.He probably mentioned the advert. on Gumtree as he knew it was a possibility you would find out, or someone would tell you.Being lonesome and missing his friendship does not take away the fact he lied to you more than once.Follow your gut instincts.You dont even have to explain it to him.