<human>: We've been dating for 3 years.

At the beginning of our relationship, I noticed my boyfriend had an attractive female friend. I asked if anything ever went on between them, and he said no. He said that he thought she was pretty but that he finds her annoying.

About a year into our relationship, I did something horrible. I snooped on his laptop and found out that he was viewing porn sites and this girl's FB pictures at the same time. I didn't think much of it because it was only one time and because I thought perhaps it was a coincidence.

Fast forward to now (2 years after I first snooped). I snooped again (horrible, I know) and found out that he's been using her pictures about twice a week, and then pictures of a few other female friends, to jerk off to. This hurts me SO much. He uses them and porn at the same time.

I won't lie, I'm an attractive female, but the other girls are probably prettier than me... And they are all the same... Big boobs, wide hips, light blue eyes, blonde hair. I have average boobs, small hips, brown eyes, and blonde hair. I've never felt insecure about my looks but all of a sudden I'm doubting everything.

I confronted him and he said he doesn't know why he does it and that he has no feelings for these girls and that it's "physical"... He said that I'm the most beautiful girl to him but I just feel like that's a fucking lie.

I have two ideas of why he does it, both lead to unhappiness for me because either...

a. he likes how they look and thinks they are hotter than me, but still loves me

or  

b. he never got to date them because they were too hot for him and wishes he was dating them but is stuck with me

This just really hurts because I thought for awhile he had some huge crush on the female he jerks off to twice a week. Now I feel like it's definitely true. Ugh help me out here reddit. :(

Can you summarize the given text in a few sentences?
<bot>: boyfriend uses pics of his attractive female friends to jerk off to... makes me feel horrible and ugly and like he wishes he was with them instead of me