If my ex ever asked me that. I'd say:

Did I ever cheat on you? I realize that I never met anyone who was even remotely interested in me. Even if someone did, I always mentioned you, not a lot, but I'd say "my GF and me went to the beach the other day". So people always got the hint I was in a relationship. Maybe that's why women stayed back? But, no, I never had anyone admit their love to me or me admit my love to them. I guess I had you as my "fill" for that department.

I do admit I was perverted on Reddit. I always left dirty comments when those chicks posted nudes in here. But after a while I realized how much of a creeper I was becoming. I just stopped.

But, I do feel like i was scared that you'd get the wrong impression when I did talk to women in general. Like I was scared that maybe you'd poison yourself thinking I was cheating on you when I added a girl on Facebook or if she texted me. Because I know how it'll look like, "girl texting him means she's interested in him".

But nah..