In my first watch through I felt really bad for Tom because at first glance it seems like he was screwed over by this one chick who just used him for entertainment and "fun" then dumped him when she grew tired of the relationship not even attempting to save it. On the second watch I noticed Tom projected a lot of his romantic feelings and dreams towards Summer which she never asked for, she does explicitly say she wasn't looking for anything serious and he disregards that and continues to pursue her love. Now with both perspectives in mind they both have some faults but in my opinion Tom was the lesser evil, he just wanted love and I don't think that's too much to ask for but he just went in the wrong direction with it. Summer however just kinda did what she felt like and was honest about it but being honest doesn't mean that it wasn't wrong.