Everyone seems to be sympathizing with Sam now, but...

Obsession and desperation aren't necessarily love. It sounds unhealthy to me. Plus, he just laid a big guilt-trip on Henry about something that happened years ago. Not cool, Sam.

And what the sister is saying - stop seeing only Sam's good qualities or making excuses for his bad ones. Look at the real Sam and make a new assessment.

I'm not saying Henry is an angel, but once you put a person in the friend-zone (for whatever reason) it's hard and scary to try and shift them into a romantic partner. Henry's "love" for Sam was a fantasy dream that he clung to. The reality isn't going to be anything like that.