<human>: Give me the gist of the text in a nutshell

F 20, M 20 
Dating for about 5 months, my first serious relationship, his second.

I made the stupid stupid mistake of reading a private message (I know it was wrong, so you can skip the scolding and finger-waving), and finding out what my boyfriend thinks of our relationship. 
He sometimes feels that he's only with me to keep from being lonely, and that he's forcing himself to stay with me. While this apparently isn't a constant thought in his head, he still thinks it sometimes. He doesn't like the fact that we don't have a lot in common, and that I want to spend a lot of time with him (he very much enjoys his alone time). Pretty much, he seems to be unsure about things and it's making me uneasy. 
He's already said "I love you" and all that, and I've said it back, meaning it 100%. We both have issues with depression, mood swings, etc. I've got trust issues, so obviously reading this set me back a bit. I feel like he's not being honest with me.
How can I ask him about all of this? I wish for some open communication between us. If he's having these thoughts, shouldn't I be able to discuss them with him? I've never been "in love" before now, but surely when you love someone, you communicate your fears and concerns..
<bot>: Read bf's private message about him being unsure about our relationship. I want to bring it up to talk it out, but don't know how to go about doing it, or if I should even bother.