We’ve been together 5 years, but lately he never wants to talk about our problems. He just kind of pushes it off, and doesn’t want to hear about my feelings. Or if I do get to express my concerns, he gets really defensive.
Not saying this is true for you, but when this happened to me he was cheating. Please check everything out. I did not want to see it.
Relationship Communication Problems : Relationship Communication Problems: Semantics

No communication, no relationship! Talking things out will only make it better, so it is impossible. Whats the point here?
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Me and my woman do the same thing.
I am living a normal life whereas she is out there modelling in posh cities.
Isn’t she beautiful
http://www.elvia-angebote.com/wp-content/uploads/2008/11/miranda_kerr_lingerie5.jpg
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Not saying this is true for you, but when this happened to me he was cheating. Please check everything out. I did not want to see it.
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I’m sorry but you can’t really have a relationship if there is no communication. I’m talking from what I know, this same incident happened to me. My ex-bf of seven years and I didnt know how to discuss anything, and that’s what caused our break-up. You guys should have a serious talk about this bc it sounds like it’s already gotten out of hand. This may not cause u guys to initially break-up but it seems to be causing problems. Just handle up on ur business, if it doesnt get any better than you should consider other options, like counseling if you really want to make it work or just kick him to the curb. Sometimes you just have to take it as a lesson learned. Good luck! Im out!
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my own experience
you say ‘lately’ so I’m assuming this hasn’t been much of a problem in the past.
He could be worried about something else at the moment, or even just going through a random phase. I’ve known both guys and girls to sometimes get defensive and closed up for a month or so before mysteriously returning to normal.
Try doing something completely out of the norm for you two: go out on a picnic, or a walk somewhere nice. It’ll jar him out of his mood a little bit.
Don’t ask him what’s wrong right away or start bringing up concerns, because that’s just going to ruin the mood.
The next day or something, tentatively try bringing up why he’s been off lately. Just ask him if everything’s been alright – because you noticed he’s been a bit closed and you’re worried. It might draw him out a little and get you two talking. Don’t focus on the problems though – if you do that a lot then he is going to get defensive because if it’s brought up often enough he’s going to feel like he’s at fault somewhere and get that ‘backed into a corner’ feeling which either leads to him getting even more defensive or to him lashing out and starting an argument.
I’m not saying to pander to him entirely, but the best way is probably to have a normal conversation and bring up the problem in a roundabout way.
Even if he doesn’t bite, having a normal, regular conversation witht he guy is going to help matter a bit because it’s some form of communication at least.
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Communication is key to a successful relationship. My 10 year marriage was on the rocks until I started couple’s/marriage therapy. r couples counseling. It helped to get my 10 year marriage back on track. Our key issue was not communicating our needs with each other. As we communicated less, spent less time together, became more distant and the communication got even worse. It was a viscous cycle. (My therapist told me that).
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http://RelationshipFrontiers.com