It sounds like you could be right about your boyfriend being depressed. The question is whether it is an attack of the 'blues'- a normal depression which will pass quite quickly and which everyone experiences from time to time - or a more severe and low state of mind - lasting much longer and which may be clinical depression.
Because of the nature of depression, it is likely to target the very resources in your relationship which can normally get you both through the difficult times - the ability to communicate, to laugh, to get distracted by happy activities.
And because you are so attuned to your partner, his negative or reduced communication will cause a hurt response in you. It can then feel very 'chicken and egg' - is it the relationship itself that is problematic - or is it depression making it problematic? This is a very common confusion when people are having relationship problems.
Many different behaviours are associated with depression. Described since Celtic times, it was Winston Churchill who popularised the term "black dog" in his frank discussion of his own depression. Even today - although we have had many public programmes normalising depression as a treatable illness - one of the big challenges is for the sufferer to separate out a self defeating sense of failure and shame - from an urgent need for help.